Sustainable, Resilient and Future Transportation

Introduction and context

Transportation enables economic activity, access to education and health care, social participation, and territorial integration. It also produces substantial environmental and social externalities. Road traffic contributes to greenhouse-gas emissions, air pollution, noise, congestion, land consumption, crashes and community severance. Aviation and shipping add significant energy and climate impacts, while transport infrastructure is exposed to floods, heat, storms, sea-level rise, landslides and other hazards.

Sustainable transportation therefore cannot be reduced to replacing petrol vehicles with electric vehicles. It requires coordinated attention to the entire mobility system: land use, travel demand, vehicle technology, energy supply, infrastructure, operations, finance, governance and social outcomes. Resilience adds the capacity to withstand, adapt to and recover from disruptions while maintaining essential accessibility. Equity asks who benefits, who bears costs and whose needs are overlooked.

For transport professionals, sustainability is a systems-design and governance challenge. A technically efficient project may be socially unjust; a low-carbon intervention may increase mineral demand or shift pollution elsewhere; and a resilient road may unintentionally encourage dispersed development and additional emissions. Sound decisions therefore require life-cycle assessment, distributional analysis, climate-risk assessment, stakeholder engagement and transparent regulatory processes.

Learning objectives

By the end of this chapter, students should be able to:

1. Explain the relationships among sustainability, resilience, accessibility, equity and transport demand.

2. Apply a systems framework to transport decarbonization and evaluate competing interventions.

3. Distinguish operational, embodied and life-cycle emissions.

4. Assess electrification, shared mobility and mobility-as-a-service critically.

5. Structure environmental, social and climate-risk assessments for transport projects.

6. Identify ethical, institutional and regulatory requirements for responsible transport governance.

7. Develop and compare future transport scenarios using appropriate indicators.

1. Foundations: from mobility to sustainable accessibility

1.1 Mobility and accessibility

Mobility describes the movement of people and goods. Accessibility describes the ease with which people can reach valued opportunities, such as employment, schools, hospitals and markets. A transport policy focused only on mobility may reward speed and vehicle throughput even when people cannot afford to travel or destinations are poorly located. Accessibility is consequently a stronger sustainability objective than movement alone.

Accessibility is influenced by three interacting components:

• Land-use distribution: where homes, jobs and services are located;
• Transport connectivity: the availability, reliability, safety and affordability of walking, cycling, public transport and motorised modes; and
• Individual circumstances: income, age, disability, gender, digital access and time constraints.

A useful planning principle is “avoid–shift–improve.” Avoid unnecessary travel and excessive trip length through integrated land-use planning; shift trips toward walking, cycling, public transport and efficient shared modes; and improve vehicles, fuels, infrastructure and operations. The hierarchy is important: efficiency improvements alone cannot offset unlimited growth in travel demand.

1.2 The three dimensions of sustainability

Environmental sustainability concerns climate change, air and water quality, biodiversity, resource use, noise and ecological integrity. Social sustainability concerns safety, health, inclusion, cultural heritage, labour conditions and fair access. Economic sustainability concerns life-cycle cost, productivity, affordability, fiscal capacity and long-term asset performance. These dimensions interact and may conflict. For example, a rail investment may deliver climate and accessibility benefits but require substantial construction materials and public expenditure.

The Sustainable Development Goals provide a broad policy context, including sustainable cities and communities, climate action, health, reduced inequalities and resilient infrastructure. They do not replace project-specific analysis; rather, they help identify the wider outcomes that transport decisions should support.

1.3 Strong and weak sustainability

Weak sustainability assumes that some losses of natural capital may be compensated by gains in produced or human capital. Under this view, a wetland might be destroyed if infrastructure benefits and ecological compensation are judged equivalent. Strong sustainability holds that certain ecological functions and social rights are non-substitutable. Critical habitats, safe climate limits and basic accessibility may therefore impose thresholds rather than merely enter a compensatory cost–benefit calculation.

Professional judgement should disclose which interpretation is being used. Monetary valuation can inform decisions, but it should not conceal irreversible damage, distributional injustice or legal rights.

2. Decarbonizing transportation

2.1 Emission sources and system boundaries

Transport emissions should be classified by source and life-cycle stage:

• Direct or tank-to-wheel emissions: emissions from fuel combustion in a vehicle;
• Energy-supply or well-to-tank emissions: emissions from extraction, processing, electricity generation and fuel distribution;
• Embodied emissions: emissions associated with materials, manufacturing, construction, maintenance and disposal; and
• Induced or indirect effects: additional travel or land-use change resulting from an intervention.

A life-cycle assessment (LCA) defines the functional unit, system boundary, inventory, impact categories and allocation rules. A suitable functional unit may be kilograms of carbon-dioxide equivalent per passenger-kilometre, tonne-kilometre or asset service-year. Comparisons are invalid if one option includes vehicle manufacture and electricity generation while another includes only tailpipe emissions.

For a vehicle or service, a simplified life-cycle greenhouse-gas expression is:

E_total = E_manufacture + E_infrastructure + E_energy + E_maintenance + E_end-of-life

where each term is measured in a common unit, usually kg CO₂-equivalent over the defined life-cycle period. The expression is an accounting identity, not a universal prediction model. It requires consistent service output, vehicle occupancy or load factor, lifetime mileage, energy mix and infrastructure allocation.

For an electric vehicle, use-phase energy emissions may be estimated as:

E_use = e × D × EF

where e is electricity consumption in kWh per vehicle-kilometre, D is lifetime distance in vehicle-kilometres, and EF is the electricity emission factor in kg CO₂-equivalent per kWh. Charging losses should be included either in e or as a separate factor, but not counted twice. The result excludes manufacturing and infrastructure emissions unless added separately.

2.2 Decarbonization pathways

A credible pathway combines several measures:

1. Demand reduction and compact development: reduce trip lengths and unnecessary vehicle travel.

2. Mode shift: improve walking, cycling, public transport, rail freight and integrated logistics.

3. Vehicle efficiency: reduce mass, aerodynamic drag, idling and energy waste.

4. Electrification: deploy battery-electric vehicles where duty cycles, charging and grid capacity are suitable.

5. Low-carbon fuels: use sustainable fuels selectively in sectors that are difficult to electrify, such as long-distance aviation and some shipping operations.

6. Operational management: optimise signals, fleet scheduling, freight consolidation and charging demand.

7. Clean energy and circularity: decarbonize electricity and improve battery, material and component recovery.

Technology substitution should be assessed against the service delivered. A full bus replacing many private car trips can have a lower per-passenger impact than a lightly occupied electric car. Conversely, an electric vehicle may not solve congestion, road danger or land-use inefficiency.

2.3 Electrification: opportunities and limitations

Electrification offers high drivetrain efficiency, zero tailpipe emissions and the possibility of using renewable electricity. It can reduce local nitrogen oxides and particulate emissions, although non-exhaust particles from tyres, brakes and road wear remain. Benefits depend on electricity generation, battery size, vehicle utilisation, lifetime, manufacturing emissions and charging behaviour.

Important implementation questions include:

• Can the distribution network support clustered charging?
• Is charging accessible to residents without private parking?
• Are battery materials sourced responsibly?
• How will batteries be repaired, reused or recycled?
• Does vehicle electrification increase vehicle size and traffic volumes?
• Are public funds being allocated equitably between private vehicles and collective transport?

Charging management can reduce peak demand by shifting charging to periods of available capacity. Vehicle-to-grid systems may provide flexibility, but they require appropriate tariffs, communication standards, battery-warranty arrangements and consumer protection.

3. Climate resilience and adaptation

3.1 Risk framework

Climate risk can be represented conceptually as a function of hazard, exposure and vulnerability. Hazard refers to the probability and intensity of an event, such as extreme rainfall or heat. Exposure describes the people, infrastructure and services located in affected areas. Vulnerability reflects susceptibility to damage and limited capacity to cope or recover. Risk is not determined by hazard alone.

A resilience assessment should:

1. identify climate variables and plausible future ranges;

2. map critical infrastructure, users and interdependencies;

3. determine failure modes and consequences;

4. identify adaptation options;

5. compare performance, cost, flexibility and residual risk; and

6. establish monitoring, maintenance and emergency procedures.

3.2 Robust, adaptive and redundant systems

A robust asset performs acceptably across a range of conditions without major modification. An adaptive system can be adjusted as conditions and information change. Redundancy provides alternative routes, modes, power supplies or communication channels. Diversity reduces dependence on a single technology or network component. Recovery planning includes emergency access, spare capacity, rapid damage assessment and restoration priorities.

Adaptation options include larger or more strategically located drainage systems, elevated or flood-resistant substations, heat-resistant pavement materials, slope stabilisation, coastal setbacks, urban shade, permeable surfaces and multimodal evacuation planning. “Build back better” should not mean rebuilding the same vulnerability; it should address the underlying failure mechanism.

3.3 Interdependencies

Transport depends on electricity, telecommunications, fuel supply, water, finance and emergency services. A flooded road may be usable physically but functionally unavailable if signals, mobile communications or charging stations fail. Network resilience therefore requires joint planning across agencies and infrastructure owners. Criticality analysis should consider not only traffic volume but also access to hospitals, emergency routes, food supply and socially vulnerable communities.

4. Environmental and social impact assessment

4.1 Environmental impact assessment

Environmental impact assessment (EIA) is a structured process for predicting effects before approval. Typical stages are screening, scoping, baseline studies, impact prediction, alternatives analysis, mitigation design, public consultation, decision-making and monitoring. A strong EIA compares alternatives, including the no-build option, rather than treating a preferred design as inevitable.

The mitigation hierarchy is:

1. avoid impacts;

2. minimise impacts that cannot be avoided;

3. restore affected environments; and

4. offset residual impacts only where appropriate and credible.

EIA should examine cumulative and indirect effects, including induced development, habitat fragmentation, construction traffic, noise, drainage alteration and carbon lock-in. Strategic environmental assessment can address policies, plans and programmes before individual projects are designed.

4.2 Social impact and distributional analysis

Social impact assessment considers displacement, livelihood effects, community cohesion, public health, cultural heritage, safety, affordability and access. Distributional analysis asks how benefits and burdens vary among income groups, locations, genders, ages, ethnic communities and people with disabilities.

Aggregate benefit does not prove justice. A road may reduce regional travel time while removing homes from a low-income neighbourhood. A congestion charge may improve air quality but burden people with limited alternatives. Mitigation may include discounted fares, improved feeder services, accessible design, relocation assistance, community benefit agreements and targeted exemptions.

4.3 Accessibility and universal design

Universal design aims for environments usable by the widest range of people without special adaptation. Transport applications include step-free routes, tactile and audible information, safe crossings, adequate lighting, seating, accessible toilets, low-floor vehicles, clear signage and interfaces compatible with assistive technologies.

Accessibility is also temporal and financial. A station may be physically accessible but unaffordable, unsafe at night or unavailable to people whose work schedules do not match service times. Accessibility audits should involve representative users and assess the complete journey, including the first and last connection.

5. Equity, ethics and professional responsibility

Transport ethics extends beyond compliance. Engineers have duties to protect public safety, disclose uncertainty, avoid discrimination, respect communities and manage conflicts of interest. A project appraisal should make value judgements visible rather than presenting them as purely technical results.

Three equity perspectives are useful:

• Distributive equity: how benefits, costs and risks are allocated;
• Procedural equity: who can participate and influence decisions; and
• Recognitional equity: whether different identities, histories, capabilities and knowledge systems are respected.

Data-driven transport creates additional ethical issues. Location data can reveal sensitive travel patterns. Automated enforcement and algorithmic pricing may reproduce bias if training data reflect unequal policing or access. AI systems should have a defined purpose, lawful data governance, explainability proportionate to risk, human oversight, cybersecurity controls and mechanisms for appeal. Predictive models should not be treated as neutral merely because they are statistical.

Professional governance should include transparent assumptions, independent review, audit trails, accessibility requirements, anti-corruption controls and clear accountability for safety-critical decisions. Public consultation is not meaningful if decisions are predetermined or technical information is inaccessible.

6. Mobility-as-a-service and shared mobility

Mobility-as-a-service (MaaS) integrates multiple modes—such as walking, public transport, bike share, car share, ride-hailing and demand-responsive transport—through common information, booking and payment interfaces. Its potential benefits include simpler transfers, better information, reduced car ownership and improved use of existing capacity.

MaaS is not automatically sustainable. Convenient ride-hailing may draw passengers from buses and trains, increase empty vehicle kilometres and intensify congestion. Digital-only services can exclude people without smartphones, bank accounts, reliable connectivity or digital confidence. Commercial platforms may control data and prioritise profitable users or routes.

Good MaaS governance requires open or interoperable standards, data protection, fare transparency, accessible non-digital channels, integration with public transport, service obligations in underserved areas and monitoring of mode substitution. Shared mobility performs best when it complements high-capacity public transport rather than replacing it.

A useful evaluation framework considers:

• passenger and vehicle kilometres by mode;
• occupancy and empty running;
• accessibility and affordability;
• reliability and transfer quality;
• emissions and energy use;
• safety and labour conditions; and
• impacts on public transport revenue and street space.

7. Scenario planning and future systems

Future transport is uncertain because of technological change, demographics, energy prices, climate impacts, policy shifts and behavioural adaptation. Forecasting extrapolates expected trends; scenario planning explores plausible alternative futures. Neither should be confused with prediction.

A scenario process may include:

1. define the decision and time horizon;

2. identify drivers and critical uncertainties;

3. construct contrasting internally consistent scenarios;

4. test transport demand, emissions, accessibility, resilience and finance;

5. identify robust strategies and signpost indicators; and

6. establish adaptive policy triggers.

Illustrative scenarios include:

• Electrified private mobility: rapid electric-vehicle uptake but continued car dependence;
• Accessible low-car city: compact development, high-quality public transport, walking and cycling, with demand management; and
• Fragmented digital mobility: extensive platform services but unequal access, weak public oversight and variable service quality.

Scenario comparison should use a multi-criteria framework rather than a single output. Criteria may include life-cycle emissions, annual operating cost, capital cost, travel time reliability, safety, social inclusion, climate robustness and institutional feasibility. Sensitivity analysis is essential because results depend on uncertain assumptions such as occupancy, electricity carbon intensity, induced demand and discount rates.

8. Economic appraisal and decision-making

Cost–benefit analysis can compare monetised benefits and costs, but it should be supplemented by multi-criteria and distributional analysis. Common benefits include travel-time savings, operating-cost changes, safety improvements, health effects, reliability and emissions reductions. Costs include construction, land, maintenance, disruption, environmental damage and administrative capacity.

Discounting converts future values to present values. The choice of discount rate can strongly affect long-lived climate and infrastructure decisions. Analysts should report sensitivity to alternative rates and avoid treating uncertain future benefits as certain. Non-monetised thresholds—such as legal air-quality limits, heritage protection or minimum accessibility—should be stated explicitly.

The correct alternative is not necessarily the one with the highest aggregate net benefit. Decision-makers must consider affordability, distribution, rights, feasibility, lock-in and the possibility of irreversible harm.

9. Illustrative case: an integrated corridor transformation

Background

Consider the fictional Riverside Corridor, a 14-km urban arterial serving 180,000 residents. It experiences daily congestion, frequent flooding at three underpasses, high roadside pollution and poor bus reliability. Outer neighbourhoods have low car ownership, while a proposed road-widening scheme would require property acquisition near a low-income community.

Problem

The authority must improve movement and climate resilience while reducing emissions, protecting vulnerable residents and maintaining emergency access. Initial proposals include road widening, battery-electric buses, a tram line and a MaaS platform.

Analysis

The project team first established a baseline covering person trips, vehicle occupancy, bus speeds, crash records, flood depths, household income, disability, air quality and access to jobs. It then modelled four alternatives: road widening; bus-priority lanes with electric buses; tram investment with compact development; and a multimodal package combining bus priority, safe cycling, flood adaptation, parking management and targeted MaaS integration.

The analysis found that road widening produced short-term vehicle-speed gains but high displacement, construction emissions and induced traffic. Electric buses reduced local combustion emissions, but benefits depended on electricity supply and depot charging. The tram alternative offered high capacity but required major capital expenditure and a long construction period. The multimodal package produced the strongest accessibility improvement per unit of public expenditure, provided that bus priority was enforced and services were frequent and affordable.

Approach and solution

The selected programme included continuous bus-priority lanes, electric buses introduced in phases, raised and protected cycle tracks, accessible pedestrian crossings, flood-resistant substations, redesigned drainage at underpasses, tree cover and shaded waiting areas, and a fare policy protecting low-income users. The MaaS application integrated public transport, bike share and demand-responsive feeder services but retained staffed ticketing and cash-compatible payment.

A community advisory panel reviewed station locations, construction impacts and relocation mitigation. Procurement required labour standards, battery end-of-life plans, open data interfaces and performance reporting. The authority established indicators for bus reliability, emissions, flood closures, accessibility, fares, crashes, mode share and distributional outcomes.

Outcome

In the first evaluation period, bus reliability and access to employment improved, while flood-related closures declined. The programme avoided major displacement and reduced traffic noise on residential streets. However, construction disruption, charging-depot costs and enforcement of bus lanes remained difficult. The case demonstrates that electrification was valuable but insufficient without priority, land-use coordination, resilience investment and social safeguards.

Learning points

1. Evaluate person accessibility, not only vehicle speed.

2. Combine avoid, shift and improve measures.

3. Treat resilience as a network and service issue.

4. Protect affordability and non-digital access.

5. Use phased implementation with measurable triggers.

6. Make trade-offs and uncertainty visible to decision-makers.

10. Implementation and best practice

A professional implementation framework should:

• define measurable outcomes before selecting technologies;
• establish a baseline and consistent system boundaries;
• compare demand management, modal and infrastructure alternatives;
• use life-cycle carbon and resource assessment;
• undertake climate-risk, EIA and social-impact assessments;
• involve affected communities early and continuously;
• design for universal accessibility and affordability;
• specify open standards, data governance and cybersecurity;
• procure for whole-life performance rather than lowest initial price;
• pilot innovations while protecting public accountability;
• monitor actual outcomes against equity and environmental indicators; and
• revise policies when evidence shows unintended effects.

No single intervention guarantees sustainability. The most defensible strategy is usually a portfolio that reduces unnecessary travel, improves collective and active modes, electrifies suitable services, manages demand, protects vulnerable groups and designs infrastructure for uncertain climatic conditions.

Challenges and limitations

Sustainability assessments face incomplete data, uncertain behavioural responses, inconsistent carbon factors, difficult valuation of health and biodiversity, institutional fragmentation and political resistance. Models may underrepresent informal travel, unpaid care trips, disabled users or people excluded from surveys. Electrification can shift impacts to electricity systems and mineral supply chains. Shared mobility can increase total vehicle travel. Climate projections contain uncertainty, but uncertainty is not a reason for inaction; it is a reason to use robust, adaptive and monitored decisions.

There are also limits to technological optimism. Digital platforms cannot substitute for adequate service funding, and autonomous vehicles do not inherently solve congestion or urban exclusion. Resilience investments may protect valuable assets while leaving vulnerable communities exposed unless distributional priorities are explicit.

Chapter Summary

Sustainable, resilient and future transportation requires a systems perspective that links accessibility, land use, modes, vehicles, energy, infrastructure, governance and social outcomes. Decarbonization should follow an avoid–shift–improve hierarchy and use consistent life-cycle boundaries. Electrification is important but depends on electricity quality, vehicle utilisation, charging access, materials and equity. Climate resilience requires assessment of hazards, exposure, vulnerability, interdependencies, redundancy and adaptive capacity. EIA and social-impact assessment should compare alternatives, address cumulative effects and apply the mitigation hierarchy. Equity includes distributive, procedural and recognitional dimensions, while ethical governance requires transparency, privacy, accountability and professional independence. MaaS and shared mobility can improve integration but require public oversight and must be evaluated for their effects on public transport, congestion and exclusion. Scenario planning, multi-criteria appraisal, phased implementation and outcome monitoring support decisions under uncertainty.

Key Terms

Sustainable transportation: Transport that meets present accessibility needs while protecting environmental, social and economic capacity for the future.

Resilience: The capacity of a transport system to withstand, adapt to and recover from disruptions.

Accessibility: The ease with which people can reach desired opportunities.

Decarbonization: Reduction and eventual elimination of net greenhouse-gas emissions.

Life-cycle assessment: Evaluation of environmental impacts across defined stages of a product, service or asset’s life.

Embodied emissions: Emissions associated with materials, manufacture, construction, maintenance and disposal.

Avoid–shift–improve: A strategy to reduce unnecessary travel, shift to sustainable modes and improve technologies and operations.

Electrification: Replacement of combustion-based energy use with electricity.

Mobility-as-a-service: Integrated planning, booking, payment and information across transport modes.

Shared mobility: Transport services in which vehicles or trips are shared among users.

Environmental impact assessment: A formal process for predicting and managing environmental effects before approval.

Social impact assessment: Analysis of effects on communities, livelihoods, health, culture and social relations.

Distributional equity: Fair allocation of transport benefits, costs and risks.

Universal design: Design usable by the widest practical range of people without special adaptation.

Climate hazard: A potentially damaging climate-related event or trend.

Vulnerability: Susceptibility to harm and limited capacity to cope or recover.

Scenario planning: Exploration of plausible alternative futures to support robust decisions.

Induced demand: Additional travel generated by improved transport capacity or reduced generalized cost.

Transport externality: A cost or benefit imposed on others that is not fully reflected in the user’s decision.

Adaptive management: Iterative policy adjustment based on monitoring, learning and changing conditions.

Review Questions

Short Answer Questions

1. Distinguish mobility from accessibility.

2. What are the three stages of the avoid–shift–improve framework?

3. Define embodied emissions and give one example.

4. Identify the three components commonly used to describe climate risk.

5. Why is electrification not, by itself, a complete sustainability strategy?

Long Answer Questions

1. Explain how life-cycle assessment can be used to compare an electric bus with a diesel bus. State the principal assumptions that must be consistent.

2. Discuss the relationship between transport decarbonization and land-use planning.

3. Explain how environmental impact assessment and social-impact assessment should influence transport project design.

4. Critically evaluate the benefits and risks of mobility-as-a-service.

5. Describe an adaptive and equitable framework for planning transport infrastructure under climate uncertainty.

Analytical / Application Questions

1. A city proposes widening a congested arterial through a low-income neighbourhood. Develop a structured alternative appraisal that considers accessibility, emissions, resilience, equity and displacement.

2. Compare a lightly occupied electric-car system with a high-occupancy electric-bus system using life-cycle boundaries, energy use, street space, accessibility and induced-demand criteria.

3. Design three contrasting 2045 transport scenarios for a metropolitan region and identify indicators and policy triggers that would reveal which scenario is emerging.

Multiple Choice Questions with Answers

Question 1

Which objective focuses most directly on people’s ability to reach employment, education and services?

A. Vehicle throughput

B. Accessibility

C. Fleet electrification

D. Road capacity

Correct Answer: B. Accessibility

Question 2

Which item is normally included in a life-cycle assessment of transport?

A. Only tailpipe emissions

B. Only travel time

C. Manufacturing and end-of-life impacts

D. Only fuel purchase price

Correct Answer: C. Manufacturing and end-of-life impacts

Question 3

In the avoid–shift–improve framework, improving public transport primarily represents which action?

A. Avoid

B. Shift

C. Improve

D. Offset

Correct Answer: B. Shift

Question 4

Which factor is not one of the three basic components commonly used to structure climate risk?

A. Hazard

B. Exposure

C. Vulnerability

D. Profitability

Correct Answer: D. Profitability

Question 5

A major limitation of vehicle electrification is that it may not eliminate which problem?

A. Tailpipe combustion emissions

B. The need for energy

C. Congestion and excessive vehicle space

D. The possibility of regenerative braking

Correct Answer: C. Congestion and excessive vehicle space

Question 6

Which principle requires impacts to be prevented before they are minimised or offset?

A. Mitigation hierarchy

B. Induced-demand principle

C. Network assignment principle

D. User-pays principle

Correct Answer: A. Mitigation hierarchy

Question 7

Which form of equity concerns who can participate in decision-making?

A. Distributive equity

B. Procedural equity

C. Technical equity

D. Operational equity

Correct Answer: B. Procedural equity

Question 8

What is a significant governance risk of a digital-only MaaS service?

A. It necessarily increases rail capacity

B. It may exclude people without digital access

C. It eliminates the need for public transport

D. It prevents all data collection

Correct Answer: B. It may exclude people without digital access

Question 9

Which approach is most appropriate when long-term transport conditions are highly uncertain?

A. Use one fixed forecast and never revise it

B. Avoid monitoring because projections are uncertain

C. Use scenarios, signposts and adaptive policy triggers

D. Select the most expensive infrastructure option automatically

Correct Answer: C. Use scenarios, signposts and adaptive policy triggers

Question 10

Which statement best describes strong sustainability?

A. All environmental losses can always be compensated monetarily

B. Natural capital is irrelevant to transport appraisal

C. Some ecological functions and social thresholds are non-substitutable

D. Only private financial returns should be considered

Correct Answer: C. Some ecological functions and social thresholds are non-substitutable