This document discusses human factors considerations for roadway design. It defines human factors as how people interact with systems, and notes its importance in designing roads, traffic controls, vehicles, and for the road user. It describes limitations in incorporating human factors into standards due to outdated data and models. Case studies demonstrate how road users seek navigational, guidance and control information differently depending on traffic conditions. Sign placement and letter height requirements are important human factor applications.

1. LOGO
Human Factors for road systems
Sudipta Sarkar
ENCI 473: Transportation Planning

2. Contents
1 What is Human Factor
2 Human Factor and Highway system
3 Limitations of humans factors incorporated into
3 standards and guidelines
44 How road users seek information
Case Study: Appropriate Sign Placement
5 and Letter Height Requirements
6 Some Human Factor Applications

3. What is Human Factor
 Human factors is the scientific discipline that studies how
people interact with devices, products, and systems.
 As applied to highway system, human factors is concerned
with the design of the roadway and operating environment
and the vehicle.

4. Human Factor and Highway System
 The road
 The traffic control
 Road user (with a
vehicle or without a
vehicle)
 Engineers can design roadways, traffic control devices, and vehicles, but they
cannot design the road user. They can design for the road user. Human
factors provides an objective basis for doing this.
 For the highway system to operate efficiently and safety, each of these
components must work together as a combined unit

5. Limitations of humans factors incorporated into
standards and guidelines
 roadways have been designed for many years while the science of
human factors was still maturing as a discipline
 Some practices are based on out-dated or inadequate behavioral data.
 Some practices are based on simple models of what road users see or
do. These models may work well for most cases but may over-simplify
other situations.
 Design equations are based on certain operational and user behaviour
assumptions and these assumptions are not always met.
 There may be particular human factors concerns for special user groups
and these concerns may have prominence for certain applications-with
the aging of the general population, there has become much greater
concern with older road users, although their needs are not fully reflected
in standards and practice.

6. How road users seek information
Road users seek information for
 Navigation-information relates to getting from point A to B
 Guidance-information relates to lane selection
 Control- related to selection of vehicle speed, level of braking , and
steering
[Alexander & Lunenfeld, 1990]

7. How road users seek information
 Road user scan the road environment seeking the most
meaningful information (MMI) for navigation, guidance and
control
 scan depends on the presence or absence of potentially hazardous
situations as they perceive them - both longitudinal and lateral
hazards.
 They develop an expectancy of the roadway based on what they
previously experienced upstream
 This searching and scanning process is continuous for the
duration of the trip

8. Examples of User-Scanned Road Environments
The following examples were prepared by showing subjects hard copies of the
roadway scenes, some with approaching vehicles and some with no approaching
vehicles (Tignor, 2006).
The subjects were asked to identify the most important information they would
consider should they confront that situation when driving.
The road is in a suburban environment and it has a speed limit of 35 mi/h.
A color code was used to prioritize the information from most to least important.
The priority of the color code was from left to right with dark green as priority one.
First Priority Last Priority

9. Examples of User-Scanned Road Environments
The following examples were prepared by showing subjects hard copies of the
roadway scenes, some with approaching vehicles and some with no approaching
vehicles (Tignor, 2006).
The subjects were asked to identify the most important information they would
consider should they confront that situation when driving.
The road is in a suburban environment and it has a speed limit of 35 mi/h.
A color code was used to prioritize the information from most to least important.
The priority of the color code was from left to right with dark green as priority one.
First Priority Last Priority

10. Example 1: User-Scanned Road Environments

11. Examples of User-Scanned Road Environments

12. Examples of User-Scanned Road Environments

13. Examples of User-Scanned Road Environments
 The first example illustrates what subjects identify as MMI when there is a
lot of activity in the road environment.
 when no vehicles are moving toward the road users many items are
identified as possible sources of meaningful information even though the
road environment has many parked vehicles, three intersections, and a
distant curve.
 The presence of approaching vehicles changes what road users consider
as important information. Approaching vehicles clearly induce the road
users to concentrate their attention to them as sources of MMI. The items
having the highest frequency of visual sources of meaningful information
are approaching vehicles, the nearest intersections, and a distant curve.

14. Examples of User-Scanned Road Environments

15. Examples of User-Scanned Road Environments

16. Examples of User-Scanned Road Environments

17. Examples of User-Scanned Road Environments
 drivers approaching a very short vertical curve that has the potential of
hiding downstream vehicles. Just upstream of the crest is a speed limit sign.
 It shows that many of the subjects look to the speed limit sign as the first or
second most meaningful source of information as opposed to the crest
beyond, which could hide a vehicle or other hazard in the roadway.
 They look at the speed limit sign whether a vehicle is or is not ahead of
them. The short vertical curve is a roadway hazard, but the speed limit sign
creates an additional hazard.
 If the road design and traffic engineering had been coordinated, more time
would have been available for the road user to seek the MMI for assessing a
potential conflict at the crest. From a safety perspective the speed limit sign
should be relocated.

18. Observations from Examples
The previous two examples show some interesting results:
 The selection process is different depending upon the presence or absence of
other vehicles. When the roadway has no other vehicles in the forward view,
the subjects’ search is longitudinally and laterally broad and downstream from
their current road location. They are primarily seeking information for guiding
and controlling the vehicle.
 When other vehicles are within their forward view, whether approaching or
traveling in the same direction, the subjects’ search is more selective. They
tend to focus first on other vehicles in the road environment and second on
information for guidance and control.
 The examples illustrate how important it is for the road design and traffic
control components to be coordinated to prevent competition for road user
attention, which compromises user safety.

19. Case Study: Determining Appropriate Sign
Placement and Letter Height Requirements

20. Some Human Factor Applications
 Sight distance determination
 Horizontal (curve) and vertical (grade) alignment determination
 Signalized intersection-Heuristics for selecting the yellow timing interval
 Roundabout-countermeasures for improving accessibility for vision-
impaired Pedestrians
 Variable message sign design
 Marking and signing design-visibility, conspicuity and consistency
requirements

21. References:
 FHWA (2003). Manual on Uniform Traffic Control Devices (MUTCD).
Washington, DC.
 Various (2010). NCHRP Report 600: Human Factors Guidelines for Road
Systems. Washington, DC: Transportation Research Board.