Traffic Engineering and Capacity Analysis

Introduction

Traffic engineering is the systematic study of the movement of people and vehicles on transportation facilities. It applies engineering principles, observation, mathematics, human-factors knowledge, and operational controls to achieve safe, efficient, economical, and environmentally responsible movement. Highway engineering is not limited to geometric design and pavement construction; a technically sound road can perform poorly if traffic demand, intersection operation, parking, pedestrians, cyclists, and control devices are inadequately considered.

Traffic engineering links three elements: demand, representing the movement users wish to make; supply, representing the road and control facilities available; and operation, representing how demand interacts with supply. The central operational relationship is:

where q is flow or volume, k is density, and v is mean speed. With q in vehicles/hour, k in vehicles/kilometre, and v in kilometres/hour, the units are consistent because (vehicles/km) × (km/h) = vehicles/h. The relationship is a basic identity for a traffic stream, but it does not by itself predict capacity or explain driver behaviour.

Traffic engineering decisions affect safety, accessibility, travel time, emissions, land use, and economic productivity. Consequently, capacity analysis should never be interpreted as a purely numerical exercise. A treatment that increases vehicle throughput may reduce pedestrian safety or transit reliability. Professional practice therefore requires both quantitative analysis and balanced judgment.

Learning Objectives

After studying this chapter, students should be able to:

1. Define and relate traffic volume, flow rate, speed, headway, spacing, density, and occupancy.
2. Distinguish time mean speed from space mean speed and select appropriate measures.
3. Explain the fundamental traffic-flow relationships and the meaning of capacity.
4. Estimate design-hour demand using appropriate adjustment factors.
5. Interpret level of service for uninterrupted and interrupted-flow facilities.
6. Analyze basic intersection capacity and perform preliminary signal timing.
7. Plan for parking, pedestrians, and cyclists.
8. Select and apply traffic-control devices using safety, consistency, and legal principles.
9. Recognize the assumptions, limitations, and ethical implications of capacity analysis.

1. Traffic-Flow Variables

1.1 Traffic volume and flow rate

Traffic volume is the number of vehicles crossing a point or section during a specified time interval. Common measures include annual average daily traffic (AADT), average annual daily traffic, daily traffic, hourly volume, and turning-movement volume.

AADT is calculated as:

AADT is useful for planning and pavement-related decisions, but it is not a direct measure of peak operating conditions. Design often uses the design-hour volume (DHV), commonly expressed as:

where K is the proportion of daily traffic occurring during the selected design hour. For a directional facility, the directional distribution factor D is also used:

Here DDHV is the design-direction hourly volume. K and D are dimensionless proportions. They must be obtained from local traffic data or an applicable design standard rather than assumed universally.

A short-period count should be converted to an equivalent hourly flow rate only when the count represents stable conditions. If V vehicles are observed during T minutes:

This is a flow-rate equivalent, not necessarily the actual volume that would occur during a full hour. It should not be used uncritically when demand varies sharply within the observation period.

The peak-hour factor (PHF) describes how evenly traffic is distributed within the peak hour:

where V_hour is the four-quarter-hour volume and V_15,max is the highest 15-minute volume in that hour. PHF ranges from 0.25 to 1.00. A value near 1.00 indicates uniform flow; a lower value indicates a concentrated peak. The peak-hour flow rate used for analysis is often:

For multi-lane facilities, additional adjustments may be needed for heavy vehicles, lane distribution, grade, and driver population.

1.2 Speed

Speed is the rate of movement of a vehicle. Important traffic-engineering measures include spot speed, running speed, journey speed, time mean speed, and space mean speed.

• Spot speed is measured at a particular location.
• Running speed excludes stopped time.
• Journey speed includes delays and stops.
• Time mean speed is the arithmetic mean of speeds observed at one point.
• Space mean speed is the average speed over a road segment and is based on travel time.

For n vehicles with speeds u₁, u₂, ..., uₙ, time mean speed is:

If the travel times over a segment of length L are t₁, t₂, ..., tₙ, space mean speed is:

Equivalently, it is the harmonic mean of individual speeds when all vehicles travel the same distance. Because faster vehicles spend less time in the observation segment, time mean speed is normally greater than or equal to space mean speed. Space mean speed is generally more appropriate for travel-time and traffic-stream analysis.

1.3 Headway, spacing, density, and occupancy

Time headway is the time between successive vehicles passing a reference point. If N vehicles pass in time T, the average headway is approximately:

where h is in seconds per vehicle if T is in seconds. Under stable conditions, flow and average headway are related by:

with q in vehicles/hour and h in seconds/vehicle.

Spacing is the distance between successive vehicles, usually measured from the same reference point on each vehicle. Density is the number of vehicles occupying a unit length of lane or roadway. Occupancy is the percentage of observation time that a detector is occupied by vehicles. Occupancy is not identical to density, although it can be used to estimate density when vehicle length and detection conditions are known.

Traffic streams may be classified as:

• Uninterrupted flow, in which traffic is influenced mainly by vehicles, roadway, weather, and incidents; examples include freeways between ramps.
• Interrupted flow, in which external controls such as signals, stop signs, or pedestrian crossings repeatedly interrupt movement.
• Mixed or multimodal flow, in which cars, buses, motorcycles, bicycles, and pedestrians interact.

1.4 Traffic composition and equivalent units

Heavy vehicles occupy more space and accelerate more slowly than passenger cars. Their effect depends on grade, length, lane width, and traffic conditions. Passenger-car-equivalent (PCE) or passenger-car-unit values may be used to convert a mixed stream into an equivalent passenger-car flow:

where v_p is adjusted passenger-car flow rate, V is observed hourly volume, N is the number of lanes or relevant capacity units, PHF is the peak-hour factor, f_HV is the heavy-vehicle adjustment factor, and f_P is a driver-population adjustment factor when applicable. The exact form and factor definitions vary by the adopted capacity manual. Factors must not be mixed between incompatible methodologies.

2. Fundamental Traffic-Flow Relationships

A useful conceptual model relates speed, density, and flow. At very low density, vehicles can travel near their desired speed, but total flow is low because few vehicles are present. As density increases, flow increases until a maximum is reached. Beyond that point, additional vehicles cause interference, reduce speed, and eventually reduce flow. The maximum stable flow is the practical meaning of capacity under specified conditions.

Figure: Conceptual flow–density relationship. The peak represents maximum flow under stated conditions.

A simple linear speed–density model is:

where v is mean speed, v_f is free-flow speed, k is density, and k_j is jam density. Combining this relationship with q = kv gives the parabolic Greenshields flow–density model:

For this particular model, maximum flow occurs at:

These equations are educational models, not universal laws. Real traffic often displays non-linear, multi-regime, hysteretic, and lane-specific behaviour. Capacity also varies with weather, incidents, access points, grades, heavy vehicles, roadway geometry, control, and driver behaviour.

3. Capacity and Level of Service

3.1 Meaning of capacity

Capacity is the maximum sustainable hourly rate at which persons or vehicles can reasonably be expected to traverse a point or uniform segment during a specified period under prevailing roadway, traffic, and control conditions. The words specified, sustainable, and prevailing conditions are essential. Capacity is not a fixed physical constant of a road.

Capacity analysis commonly distinguishes:

• Basic capacity, under ideal or reference conditions.
• Practical or operational capacity, associated with acceptable service quality.
• Design capacity, selected with consideration of demand, reliability, risk, and policy.

A facility can have adequate theoretical capacity but poor operation because of queues, access friction, unsafe crossings, poor signal coordination, or unreliable travel times.

3.2 Level of service

Level of service (LOS) is a qualitative description supported by quantitative measures such as speed, density, delay, volume-to-capacity ratio, queue, and reliability. Traditionally, LOS A represents very favourable operating conditions and LOS F represents breakdown, excessive delay, or demand exceeding available capacity. LOS labels are not identical across facility types; an acceptable delay at a signalized intersection cannot be directly compared with freeway density without reference to the appropriate methodology.

For uninterrupted flow, density and speed may be central measures. For signalized intersections, control delay, queue, progression, and volume-to-capacity ratio are important. For pedestrians and cyclists, comfort, delay, crossing exposure, effective width, conflicts, and perceived safety may be more meaningful than vehicle throughput.

The volume-to-capacity ratio is:

where v is demand flow rate and c is capacity, expressed in identical units. X below 1 does not guarantee no queue: short-term variation, residual queues, poor progression, and arrival patterns can still create delay. As X approaches or exceeds 1, queues become increasingly unstable unless demand is temporary and storage is sufficient.

LOS should support, not replace, engineering judgment. A design standard may prescribe thresholds, but the selected target should reflect road function, land use, safety, public transport, emergency access, and community objectives.

4. Intersection Capacity and Basic Signal Timing

4.1 Signalized intersection concepts

A traffic signal allocates right-of-way among conflicting movements. Its principal timing terms are:

• Cycle length (C): time for one complete sequence of signal indications.
• Phase: a portion of the cycle assigned to a movement or compatible movement group.
• Green time (G): displayed green interval.
• Yellow change interval: warns that the right-of-way is ending.
• Red clearance interval: permits vehicles within the intersection to clear before conflicting green.
• Effective green (g): operational green available after accounting for start-up and clearance effects.
• Lost time (L): time in a cycle not effectively used by moving traffic.

For a lane group with saturation flow s and effective green g, an elementary capacity estimate is:

where c and s are in vehicles/hour of green or vehicles/hour, and g/C is dimensionless. This simplified equation assumes stable saturation discharge, a correctly defined lane group, and no blocking or unusual downstream restriction. Professional capacity manuals include adjustment factors for lane utilization, heavy vehicles, grades, parking, pedestrian activity, turning movements, and permitted conflicts.

A practical preliminary timing procedure is:

1. Identify phases and conflicting movements.
2. Determine approach volumes and lane groups.
3. Estimate saturation flow and lost time using the applicable standard.
4. Calculate critical flow ratios yᵢ = vᵢ/sᵢ.
5. Sum critical ratios to obtain Y.
6. Select a cycle length considering delay, coordination, pedestrian clearance, and storage.
7. Allocate effective green approximately in proportion to critical flow ratios.
8. Check queues, pedestrian service, coordination, safety, and clearance intervals.

A simplified Webster-type optimum cycle estimate is:

where C₀ is an estimated cycle length in seconds, L is total lost time per cycle in seconds, and Y is the sum of critical flow ratios. The equation is applicable only to preliminary isolated-intersection analysis under assumptions associated with the model. It becomes unsuitable when Y approaches 1, oversaturation exists, pedestrian timing governs, coordination is required, or unusual arrival patterns dominate. The final cycle must comply with the adopted traffic-control standard and field conditions.

Worked example: preliminary signal timing

An isolated two-phase intersection has critical flow ratios y₁ = 0.28 and y₂ = 0.36. Total lost time is 8 s per cycle. Then:

A preliminary cycle of approximately 47 s may therefore be considered. If effective green is allocated proportionally after lost time:

The effective greens sum to 39.2 s, equal to C₀ − L. These are not final display settings. Yellow, all-red, pedestrian clearance, minimum greens, detector operation, and legal requirements must be checked before implementation.

For an unsignalized intersection, capacity depends on acceptable gaps, conflicting flow, critical gap, follow-up headway, sight distance, and priority rules. Signalization should not be selected solely because a volume threshold is exceeded; crash history, vulnerable users, network effects, and alternative treatments must also be evaluated.

5. Traffic-Control Devices

Traffic-control devices communicate rules, warnings, and guidance. Their design should follow five principles: need, uniformity, conspicuity, legibility, and credibility. Devices should be placed where users can perceive, understand, and respond to them safely.

The principal classes are:

• Regulatory devices: establish legal requirements, such as speed limits, stop, yield, turn restrictions, and parking restrictions.
• Warning devices: alert users to hazards or changes requiring caution.
• Guide and information devices: provide route, destination, lane, service, and traveler information.
• Pavement markings: allocate lanes, separate opposing traffic, define edges, indicate stop lines, crossings, and bicycle facilities.
• Temporary traffic-control devices: manage work zones and altered road conditions.

Signs and markings must be consistent with the jurisdiction’s traffic-control manual and legal framework. Excessive signs reduce attention and credibility. Variable-message signs and connected systems can improve incident management, but information must be accurate, timely, accessible, and protected against failure or cyberattack. Automated enforcement requires transparent legal authority, calibrated equipment, due process, privacy safeguards, and equitable implementation.

6. Parking, Pedestrian, and Cyclist Needs

6.1 Parking

Parking analysis considers demand, duration, turnover, accumulation, occupancy, supply, and location. Turnover is the number of vehicles using a space during a period. Occupancy is the proportion of spaces occupied at a specified time. A parking facility may have adequate total supply but still fail if spaces are poorly located, inaccessible, or occupied for excessive durations.

Parking design should address:

• on-street and off-street supply;
• access, circulation, aisle width, and manoeuvring;
• accessible spaces and routes;
• loading, deliveries, emergency access, and fire safety;
• visibility at driveways and intersections;
• drainage, lighting, security, and pedestrian routes;
• pricing and time controls;
• effects on transit, cycling, and public space.

On-street parking can support access and traffic calming but reduces effective roadway width and sight distance. Near intersections, crossings, and cycle facilities it can create serious visibility conflicts. Parking restrictions should be based on observed demand, safety, operations, and land-use objectives rather than habit alone.

6.2 Pedestrians

Pedestrian planning begins with the principle that walking is a legitimate mode, not an obstruction to motor traffic. Continuous accessible footways should connect homes, schools, transit stops, employment, and public facilities. Important design factors include effective width, surface quality, slope, drainage, lighting, crossing distance, refuge, signal timing, accessibility, and personal security.

The effective width of a footway is less than its physical width when street furniture, signs, trees, walls, poles, or parked vehicles create shy distances. Crossings should be located on natural desire lines and should provide adequate sight distance. Curb ramps, tactile indicators, audible signals, and appropriate grades support users with disabilities.

Pedestrian signal timing must provide sufficient walk and clearance time. A simplified clearance calculation is:

where t_c is clearance time in seconds, W is crossing distance in metres, and v_p is the selected pedestrian walking speed in metres/second. The selected speed must follow local standards and should account for older adults and users with mobility limitations. Signal design may also require start-up time, buffer intervals, median refuge, and detectable warnings.

6.3 Cyclists

Cyclists need a connected, continuous, legible, and low-conflict network. Facility selection depends on speed, volume, heavy-vehicle activity, available width, intersection form, parking, and user skill. Treatments include shared lanes, bicycle lanes, separated tracks, bicycle boulevards, and off-road paths. At intersections, conflict reduction is usually more important than uninterrupted vehicle progression.

Design should provide adequate operating width, safe transitions, drainage grates aligned with travel, appropriate surface quality, parking-protection zones where justified, and clear priority. Bicycle facilities should not terminate abruptly at a major conflict point. Signal detection must recognize bicycles, and signal phasing should avoid trapping riders in turning conflicts.

7. Applied Case: Safety and Capacity at a School Corridor

Background

The following is an illustrative case. A four-lane urban arterial passes a secondary school and transit stop. The road carries an AADT of 24,000 vehicles/day. The observed weekday peak-hour volume is 2,160 vehicles/hour, with 60% travelling in the school-bound direction. A signalized crossing is 90 m from the school gate. Parents frequently stop on the approach, cyclists merge into traffic, and students cross at an unsignalized desire line.

Problem

Vehicle delay is moderate, but the corridor has pedestrian conflicts, blocked sight distance, irregular parking, and a history of near misses. A proposal to increase green time for the arterial would improve motor-vehicle progression but might lengthen pedestrian waiting and increase crossing risk.

Analysis

The directional peak-hour demand is:

A manual count shows a 15-minute maximum of 600 vehicles during the peak hour. The PHF is:

The equivalent peak 15-minute flow rate is therefore:

This reveals a concentrated demand that an hourly average alone would hide. Field observation also identifies school arrival surges, bus stopping, and illegal parking as operational constraints. A vehicle-only capacity calculation would not capture these risks.

Approach and solution

A multimodal treatment is selected:

1. Relocate the crossing to the school desire line and provide a raised or highly visible crossing treatment where permitted.
2. Install curb extensions or protected refuge, subject to emergency and drainage checks.
3. Prohibit stopping near the crossing and enforce the restriction during school arrival and departure.
4. Provide a continuous protected cycling connection through the conflict area.
5. Coordinate the signal with school arrival periods while preserving minimum pedestrian timing.
6. Mark a signed loading zone away from the crossing.
7. Use counts and conflict observations before and after implementation.
8. Review speed management, lighting, accessibility, and winter maintenance.

Outcome

In this illustrative evaluation, post-treatment observations show shorter crossing distances, fewer illegal stops, improved pedestrian compliance, and more reliable bus operation. The arterial green time is not maximized; instead, the signal is operated to balance corridor throughput with safe and accessible crossing service. The result demonstrates that the best traffic-engineering solution is often a network and safety solution rather than a capacity-only solution.

Learning points

• Directional distribution and PHF reveal conditions hidden by daily totals.
• Delay is only one performance measure.
• Parking control can improve effective capacity and safety simultaneously.
• Pedestrian and cyclist requirements must be included at the beginning of analysis.
• Before-and-after evaluation is necessary because predicted performance is uncertain.

8. Data, Technology, and Contemporary Practice

Traditional tube counts, manual turning counts, radar, video, Bluetooth or Wi-Fi re-identification, automatic number-plate recognition, connected vehicles, and mobile-device data can support traffic studies. Each source has sampling bias, privacy, calibration, and reliability issues. Video analytics and artificial intelligence can classify vehicles, detect queues, identify near misses, and support adaptive signals, but results require validation against field observations. A model that performs well in daylight may fail in rain, glare, occlusion, or unusual traffic.

Intelligent transportation systems include adaptive signal control, ramp metering, incident detection, variable speed limits, traveler information, transit priority, and integrated corridor management. Their purpose should be defined before technology is selected. More data do not automatically produce better decisions; agencies need documented data governance, cybersecurity, retention limits, public transparency, and procedures for correcting errors.

Climate change and resilience also affect capacity. Flooding, heat, smoke, snow, extreme rainfall, and power failures alter speed, visibility, road availability, and signal operation. Resilient practice includes backup power, emergency operating plans, drainage maintenance, redundant communications, and designs that remain usable by pedestrians and cyclists during disruptions.

9. Limitations, Ethics, and Best Practice

Capacity models simplify human behaviour and physical conditions. Their limitations include uncertain demand forecasts, changing land use, non-recurrent incidents, heterogeneous vehicles, imperfect detector data, unstable queues, and differences between calibrated and default parameters. Analysts should report assumptions, data dates, confidence limitations, sensitivity results, and the consequences of uncertainty.

Ethical practice requires that safety and accessibility not be sacrificed to achieve a numerical LOS target. Analysts should consider whether a project disproportionately burdens children, older adults, disabled users, low-income communities, or people without cars. Enforcement and automated data collection should be lawful, proportionate, auditable, and privacy-respecting. Public consultation is particularly important when parking removal, road reallocation, or signal changes affect local access.

A robust workflow is:

1. Define the decision, study area, users, and evaluation period.
2. Collect and quality-check volumes, speeds, crashes, queues, parking, and multimodal observations.
3. Select a method appropriate to the facility and local standard.
4. Establish existing conditions and calibrate where possible.
5. Develop alternatives, including demand management and non-motorized options.
6. Test operations, safety, accessibility, resilience, and distributional effects.
7. Document assumptions and perform sensitivity analysis.
8. Implement with monitoring, maintenance, and post-project evaluation.

Chapter Summary

Traffic engineering analyzes how demand interacts with roadway, intersection, control, and multimodal facilities. The fundamental identity q = kv connects flow, density, and speed, while headway, spacing, occupancy, PHF, and directional distribution describe the operational stream. Time mean speed and space mean speed have different meanings and must not be interchanged.

Capacity is a sustainable rate under specified conditions, not a universal constant. Level of service provides a structured description of operating quality, but it must be interpreted with safety, accessibility, reliability, land use, and public policy. Signal capacity depends on saturation flow and effective green, while preliminary timing requires critical flow ratios, lost time, pedestrian requirements, and field validation.

Effective traffic control depends on uniform, credible, visible, and legally appropriate devices. Parking, pedestrian, and cycling provisions are integral components of highway performance. Modern data and artificial intelligence can improve monitoring and control, but they introduce privacy, validation, cybersecurity, and governance responsibilities. The strongest professional practice combines sound calculations with multimodal observation, transparent assumptions, ethical judgment, and post-implementation evaluation.

Key Terms

Traffic volume: Number of vehicles passing a point or section during a specified period.

Flow rate: Equivalent hourly rate of traffic movement, often derived from a shorter observation.

AADT: Average annual daily traffic over all days of a year.

Design-hour volume: Traffic volume selected for design during a specified critical hour.

Peak-hour factor: Measure of the uniformity of traffic within the peak hour.

Time mean speed: Arithmetic mean of vehicle speeds observed at one point.

Space mean speed: Average speed over a road segment based on travel time.

Headway: Time interval between successive vehicles passing a point.

Spacing: Distance between successive vehicles in a traffic stream.

Density: Number of vehicles occupying a unit length of roadway.

Occupancy: Proportion of detector observation time occupied by vehicles.

Capacity: Maximum sustainable hourly rate under specified conditions.

Level of service: Qualitative description of operating conditions supported by performance measures.

Saturation flow: Rate at which vehicles discharge during effective green under prevailing conditions.

Effective green: Portion of a signal cycle effectively available for traffic discharge.

Lost time: Cycle time not effectively used by moving traffic.

Critical flow ratio: Demand flow divided by saturation flow for a critical lane group.

Peak-direction factor: Proportion of total demand travelling in the design direction.

Passenger-car equivalent: Factor representing the effect of a vehicle class relative to a passenger car.

Traffic-control device: Sign, signal, marking, or other device used to regulate, warn, or guide users.

Review Questions

Short Answer Questions

1. Distinguish traffic volume from flow rate.
2. Why is space mean speed generally more useful than time mean speed for traffic-stream analysis?
3. Define capacity and explain why it is not a fixed property of a road.
4. What does a peak-hour factor of 0.90 indicate?
5. Identify four principles governing effective traffic-control devices.

Long Answer Questions

1. Explain the relationships among flow, speed, and density, including the assumptions and limitations of the Greenshields model.
2. Describe the procedure for preliminary signal timing at an isolated intersection.
3. Discuss how parking affects roadway capacity, safety, and pedestrian movement.
4. Explain how LOS differs for uninterrupted flow, signalized intersections, pedestrians, and cyclists.
5. Discuss ethical and governance issues associated with automated traffic data and enforcement.

Analytical / Application Questions

1. A road records 1,800 vehicles in the peak hour and 520 vehicles in its highest 15-minute interval. Calculate the PHF and equivalent peak-hour flow rate, showing units and interpretation.
2. A two-phase signal has critical flow ratios of 0.25 and 0.40 and total lost time of 10 s. Use the preliminary Webster-type equation to estimate cycle length and discuss whether the result can be adopted directly.
3. Develop a multimodal improvement strategy for a high-volume arterial beside a school where vehicle delay is acceptable but pedestrian crashes and illegal parking are increasing. Identify data required, alternatives, evaluation measures, and implementation risks.

Multiple Choice Questions with Answers

Question 1

Which equation expresses the basic relationship among flow, density, and speed?

A. q = k v

B. q = k ÷ v

C. q = v ÷ k

D. q = k + v

Correct Answer: A. q = k v

Question 2

A four-quarter-hour volume is 2,000 vehicles and the highest 15-minute volume is 600 vehicles. What is the PHF?

A. 0.72

B. 0.83

C. 0.90

D. 1.20

Correct Answer: B. 0.83

Question 3

Which speed measure is based on travel time over a road segment?

A. Spot speed

B. Time mean speed

C. Space mean speed

D. Running speed only

Correct Answer: C. Space mean speed

Question 4

If average headway is 3 seconds per vehicle, the corresponding flow rate is approximately:

A. 600 vehicles/hour

B. 900 vehicles/hour

C. 1,200 vehicles/hour

D. 3,600 vehicles/hour

Correct Answer: C. 1,200 vehicles/hour

Question 5

In the simplified signal-capacity equation, c = s × (g ÷ C), the ratio g ÷ C represents:

A. Lost time

B. Effective green proportion

C. Heavy-vehicle percentage

D. Directional distribution

Correct Answer: B. Effective green proportion

Question 6

What does a volume-to-capacity ratio greater than 1 generally indicate?

A. Demand exceeds available capacity

B. Free-flow operation is guaranteed

C. No queue can form

D. The PHF equals 1.0

Correct Answer: A. Demand exceeds available capacity

Question 7

Which factor most directly describes concentration of traffic within a peak hour?

A. AADT

B. PHF

C. Jam density

D. Parking turnover

Correct Answer: B. PHF

Question 8

Which treatment most directly improves pedestrian crossing accessibility?

A. Increasing lane width only

B. Removing all crossing markings

C. Providing curb ramps and detectable warnings

D. Increasing the arterial speed limit

Correct Answer: C. Providing curb ramps and detectable warnings

Question 9

For the illustrative case, if 60% of 2,160 peak-hour vehicles travel in one direction, the directional volume is:

A. 864 vehicles/hour

B. 1,080 vehicles/hour

C. 1,296 vehicles/hour

D. 2,160 vehicles/hour

Correct Answer: C. 1,296 vehicles/hour

Question 10

Which statement about traffic-control devices is correct?

A. More signs always improve safety

B. Devices should be uniform, credible, visible, and needed

C. Legal authority is unnecessary for regulatory signs

D. Temporary devices need not be consistent with permanent controls

Correct Answer: B. Devices should be uniform, credible, visible, and needed