REPORTING 2: CHARACTERISTICS OF THE DRIVER, PEDE STRIAN, BICYCLIST, VEHICLE, AND THE ROAD

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DRIVING CHARACTERISTICS

Drivers have varying skills and perceptual abilities (seeing, hearing, evaluating, reacting). Abilities may change under alcohol, fatigue, or time of day. Engineers must design for most drivers' capabilities while balancing costs. 85th to 95 Percentile often used in setting design criteria.

VISUAL ACUITY

The ability to see fine details of objects along a direct line of vision. Measured using the Snellen Eye Chart or 6/6 20/20 Vision. Determines how far signs can be read depending on visual acuity. Important in traffic sign size & placement

STATIC ACUITY

Stationary objects, Background Brightness, Contrast, Time

DYNAMIC ACUITY

Moving objects, 3o-5o Cone - Clear Vision, 10o-12o Cone - Fair Vision

PERIPHERAL VISION

Ability to see objects outside the cone of clearest vision. Peripheral field can extend up to 160o. Example: Detecting a vehicle approaching from the side.

SPEED & AGE

FACTORS AFFECTING PERIPHERAL VISION

SPEED

Higher speeds reduce effectiveness

AGE

Significant reductions around 60 years old

COLOR VISION

Ability to differentiate one color from another. Not a major issue in driving - drivers can rely on the shape and position of signs/signals.

APPLICATIONS OF COLOR VISION

High-contrast combinations (e.g., black & white, black & yellow) are most visible. These are widely used in warning and regulatory signs.

GLARE VISION AND RECOVERY

DIRECT GLARE

Bright light directly in field of vision (e.g., headlights) It is imperative for LTO to regulate installed headlights

SPECULAR GLARE

Reflection of bright light (e.g., sun on windshield)

EFFECTS OF SPECULAR GLARE

Reduced visibility & eye discomfort, Sensitivity increases with age (notable after 40)

GLARE RECOVERY

Crucial for night driving, especially older drivers. ~3s - dark to light. ≥6s - light to dark

DESIGN CONSIDERATIONS

Reduce luminaire brightness. Increase background brightness. Apply higher mounting heights, setbacks, glare shields, or vegetated medians

DEPTH PERCEPTION

Ability to see in 3D and estimate speed and distance.

Importance in Driving of Depth & Perception

Critical for passing and turning maneuvers. Poor judgment increases crash risk.

Human Eye Limitations

Not accurate at estimating absolute speed, distance, size, acceleration.

Traffic Control Devices

Standardized size, shape, color leads to easier recognition. Helps both normal and color-blind drivers

HEARING PERCEPTION

The EAR - detects sound stimuli

Importance in Driving of Hearing & Perception

Mainly for warning sounds (e.g., sirens of emergency of emergency vehicles)

Hearing Loss

Not a major problem for driving and often corrected with hearing aids

IMPACT ON DRIVING OF OLDER DRIVERS' CHARACTERISTICS

Difficulty reading and interpreting road signs in time, Longer glare recovery → missed signals or obstacles at night, Delayed reactions increase crash risk, especially in emergencies, Higher vulnerability in work zones, intersections, and heavy traffic

DESIGN CONSIDERATIONS

Larger, clearer, and more legible signage, Minimized glare in roadway lighting, Age-friendly roadway and intersection design, Special attention to work zones and complex traffic environments

PERCEPTION

Noticing objective/device

IDENTIFICATION

recognizing/understanding

EMOTION

Choosing response (brake, swerve, etc.)

REACTION

Carrying out action

PIEV Time

Total time from perception to reaction

IMPORTANCE OF PIEV TIME

determines braking distance, sight distance, yellow signal timing

INFLUENCING FACTORS OF PIEV TIME

Situation complexity & driver training, Environment: weather, lighting, Human factors: age, fatigue, alcohol/drugs, Expectation (expected vs. unexpected events)

OBSERVED RANGES

Expected: 1.0 - 5.1 secs ; Unexpected: 1.6 - 7.8 secs ; Expectation - most critical factor ; On average, 5 seconds is used in actual practice for

PIEV TIME DESIGN STANDARD (AASHTO)

2.5 secs (covers ~90% of drivers). May be inadequate for unexpected or complex situations (e.g., multiphase signals, ramps)

PEDESTRIAN CHARACTERISTICS

Pedestrians share similar visual & hearing limits as drivers. Additional characteristics affect design of control devices:

SIGNALS

timing for walk/clearance phases

SAFETY ZONES & ISLANDS

safe refuge at intersections

UNDERPASSES & ELEVATED WALKWAYS

Underpasses & elevated walkways. Separating conflicts

CROSSWALKS

Walking characteristics are especially important in signal timing

WALKING SPEEDS & DESIGN VALUES

Observed walking speed range: 0.9 - 2.4 m/s

Mean speeds at intersections:

Males - 1.5 m/s ; Females - 1.4 m/s

PEDESTRIAN DESIGN STANDARDS

Conservative Value - 1.22 m/s ; Elderly Share > 20% - 0.9 m/s ; Predominantly Elderly (65+) - 0.88m/s

SPECIAL CONSIDERATIONS FOR ELDERLY PEDESTRIANS

Elderly pedestrians: slower speeds, narrower vision → safer timing needed

Handicapped Pedestrians

Accessible Pedestrian Signals (APS) devices (audible, speech, vibration cues) ; Curb ramps for wheelchairs ; Walking speed: 0.6-1.12 m/s

MUTCD guideline

use 1.07 m/s (instead of 1.2 m/s) for pedestrian interval

BICYCLES IN THE HIGHWAY SYSTEM

Bicycles are now a key urban transportation mode alongside cars and transit. Highway & traffic engineers must understand both vehicle and rider characteristics

BICYCLIST

Both driver and power source, forming a single human-machine system. Human factors (perception, reaction time, decision making) apply, but with added physical demands (balance, pedaling effort)

Bicycle use by purpose

commuting, recreation, school, and errands → requires safe, accessible facilities

BICYCLIST CLASS A

Experienced and Advanced Bicyclists. Comfortable in traffic, treat bike like a car

BICYCLIST CLASS B

Less Experienced. Prefer neighborhood streets & designated bike paths. not applicable for highway design and are used more on urban roads

BICYCLIST CLASS C

Children/Novice. Ride mostly on residential streets, near schools/parks. not applicable for highway design and are used more on urban roads

Experienced & Confident

Alternative Classification (TOOLE DESIGN): Ride on almost any facility; commuters, club riders. Speed: 32 km/h (flat) and 72 km/h (downhill)

Casual & Less Confident

Alternative Classification (TOOLE DESIGN): Majority of riders; prefer safe, low-volume, or dedicated facilities. Speed: 12-20 km/h

BICYCLIST DESIGN CONSIDERATION

Visible, connected bicycle facility network to encourage more riders

STATIC, KINEMATIC, DYNAMIC

Three major vehicle characteristics that the geometric design of highways generally consider

DESIGN VEHICLE

Due to varying vehicle characteristics, a ______________ is considered to encompass all the necessary features needed for highway design

BRIDGE FORMULA

The new law passed also included a requirement for the computation of the maximum gross weight of two or more consecutive axles. W=230 (LNN-1+23N+36)

BRIDGE FORMULA

Enacted in 1975 to limit the weight-to-length ratio of vehicles passing a bridge. As vehicles got heavier, officials had the need to think of a solution to regulate the passing of vehicles, thus the weights became dependent on the number and spacing of axles from one another (US Department of Transportation, Federal Highway Administration, 2019).

15,400 kg ; 11 m

A maximum gross load of ______ kg may be carried by two consecutive sets of double axles when the distance between the first and last axle of both groups is __ m or more.

Truck Weights for those who wish to pass bridges

Gross weight should not exceed 36,500 kg; Weight applied on a single axle should not exceed 9,100 kg; and Weight applied on a double axle should not exceed 15,400 kg

DESIGN VEHICLE SELECTION

States are no longer allowed to set length limits on trucks, since static characteristics are used for selecting highway design criteria. Thus

Passenger Cars, Buses, Trucks, Recreational Vehicles

AASHTO has classified four general vehicle types, which are:

DESIGN VEHICLES

Determines the design of roadway elements. Designer should accommodate largest design vehicle that would utilize the roadway being designed. If a larger vehicle uses the road facility, its size should be the one to govern and not the minimum design vehicle size measurement

CONTROL VEHICLES

infrequent large vehicles that are rarely accommodated by the roadway

16 KPH

For every intersection, the turning radii at speeds of __ kph must be provided, which are highly dependent on the size of the vehicle.

AASHTO's Policy on Geometric Design of Highways and Streets

provides a complete list of turning radii for different vehicles

Transition Curve Length

As vehicle speed increases, ____________________ increases as well.

ACCELERATION CAPABILITY

It is the main primary element in Kinematic Characteristics calculations of design vehicles. The capability of a design vehicle to accelerate, alongside its effects to its time of travel, distance travelled, and speed dictates numerous highway design features such as width of ramps and overtaking lanes, etc

AIR RESISTANCE

Force required to overcome air resistance as the vehicle moves through air. Includes resistance from air in front of the vehicle and frictional action around it. Can be estimated using Claffley Formula.

GRADE RESISTANCE

Force component of vehicle weight acting opposite to motion on inclined surfaces. Affects speed achievement and requires compensating acceleration force.

ROLLING RESISTANCE

Sum of internal vehicle forces that resist motion. Frictional effects on moving vehicle parts

CURVE RESISTANCE

Retarding force components acting on vehicle when navigating curves

Influencing Factors for CURVE RESISTANCE

External forces on front wheels during maneuvering ; Curve radius ; Vehicle gross weight ; Vehicle velocity

POWER REQUIREMENTS

Rate of work done to overcome resistance forces (measured in horsepower). Performance capability measured by engine horsepower output.

1 horsepower = 746 N-m/s or W

Watt Equivalent of Horsepower is?

BRAKING DISTANCE

Horizontal distance required for a vehicle to come to complete stop, considering all resistance forces and driver reaction time

Physical Forces, Human Factor, Vehicle Dynamics

Key Components of Braking Distance

PHYSICAL FORCES

Key Component o Braking Distance regarding: Air, Grade, Rolling, and Curve resistance

HUMAN FACTOR

Key Component o Braking Distance regarding: Perception-reaction time delay

VEHICLE DYNAMICS

Key Component o Braking Distance regarding: Friction coefficient, center of gravity, vehicle track width

ESTIMATE OF VELOCITIES

Estimate the speed of a vehicle just before it is involved in a crash

a maximum of 0.10

Superelevation Rate for Rural areas with no snow or ice

0.08 to 0.10

Superelevation Rate for Areas with snow and ice

maximum of 0.08

Superelevation Rate for Expressways in urban areas

usually not superelevated

Superelevation Rate for Expressways in urban areas

SIGHT DISTANCE

It is the length of the roadway a driver can see ahead at any particular time.

Stopping sight distance, Decision sight distance, Passing sight distance

Three types of Sight Distance

STOPPING SIGHT DISTANCE (SSD)

Minimum sight distance required for a driver to stop a vehicle after seeing an object in the vehicle's path without hitting that object. This distance is the sum of the distance traveled during perception-reaction time and the distance traveled during braking.

The same as the stopping distance

The SSD for a vehicle traveling at u km/h is?

DECISION SIGHT DISTANCE (DSD)

Distance required for a driver to detect an unexpected or otherwise difficult to perceive information source or hazard in a roadway environment that may be visually cluttered, recognize the hazard of its threat potential, select an appropriate speed and path, and initiate and complete the required safety maneuvers safely and efficiently (AASHTO). The DSDs depend on the type of maneuver required to avoid the hazard on the road, and also on whether the road is located in a rural or urban area

PASSING SIGHT DISTANCE (DSD)

Minimum sight distance required on a two-lane, two-way highway that will permit a driver to complete a passing maneuver without colliding with an opposing vehicle and without cutting off the passed vehicle. Allow the driver to successfully abort the passing maneuver if he or she desires.