EFECTO DE LOS ELEMENTOS ALEANTES

Improper behaviour of pedestrians and drivers is the direct reason for pedestrian accidents, besides subjective reasons of road users, the objective problems like poor visibility and signal control deficiencies contribute to the risky behaviour and accidents as well.

Improper pedestrian behaviour

(1) Pedestrian non-compliance is the dominant reason for pedestrian accidents.

About one-third of fatal crashes involving pedestrians resulted from pedestrians disobeying signals or making misjudgement while attempting to cross (NHTSA, 2000). Pedestrian false behaviour (e.g. signal violation) is claimed to be the 7th important reason for accidents with injuries in Germany, counting about 10% (Statistic year book, 2008). Statistical data in China shows that pedestrian signal violation contributes to about 17% pedestrian fatalities (CRTAS, 2005~2007). Meanwhile, previous studies on demographic characteristics of pedestrian behaviour (cf. 2.2.2.2) and accidents (cf. 3.1.2) revealed a consistent relationship of each other.

(2) Pedestrian improper “visual search behaviour” contributes to accidents with turning vehicles. Pedestrians attempted very little visual search for turning vehicles when crossing at a signalised intersection, especially for vehicles coming from behind (Lord, 1997). “… pedestrians tended to

3.2 Pedestrian accident analysis 29

search for potential threats during the DON’T WALK phase, but they did not search during the WALK phase” (Jennings, 1977).

Turning vehicles fail to yield to pedestrians

Pedestrian accidents happened with turning vehicles can be largely attributed to turning vehicles failing to yield to pedestrians. As mentioned by Andree (2007), the main risk for pedestrians at signalised intersections is the conflicts between pedestrians and turning vehicles, more serious is with left-turning vehicles or high speed right turning vehicles.

Visibility problems of vehicles and (or) pedestrians

• Visibility relates to photometric concerns, most important ones are “the visual size, the contrast with the background, the ambient light levels, the presence of glare, the colour etc.” (Hills, 1980; Langham, 2003), which helps to explain that more accidents happened in winter time and late afternoon.

• Too small number of pedestrians, e.g. a single pedestrian is easy to be neglected (Lord, 1994).

• Parking vehicles or stationary vehicles on adjacent lanes (Craddock, 1992), particularly the space near to crossings are occupied by buses or trucks, will impede visibility of both pedestrians and drivers.

• Other physical visual impediments such as too high vegetation in the centre stripe affects on visibility negatively.

• The speed of vehicles should be taken into account, corresponds to the moving obstacles defined by Gibson and Crooks (1938), especially for left turning vehicles.

Signal control deficiencies

A study by Craddock (1992) mentioned if the following two features are present at the same time, concealed or misleading vehicle movements and unsaturated flow of vehicles, a major cluster of pedestrian accidents may be generated. Situations leading concealing or misleading movement include “asynchronous signalisation of lanes at the same stop line”, “turning movements held by opposing flow”, “vehicles queuing over a signalised crossing” and “different directional timing for traffic”.

Thirteen types of “latent danger” developed by Häckelmann (1976) (Table 4), most of which are related to signal control, were claimed to contribute to pedestrian accidents at signalised intersections significantly. It was found that 80% accidents were led by latent dangers, and in which 21% with too long clearance time for pedestrians; 42% with too long red time for pedestrians, at least longer than 60s; 43% with tram station or bus stop nearby; 16% with improper intergreen time; 16% with short green time for pedestrians.

Table 4: “Latent danger (LD)” for pedestrians at signalised intersections

No. Latent danger

LD 1 too long red-amber time for vehicles while big adopted clearance speed of pedestrians

LD 2 separated signal control for vehicles of different lanes LD 3 too long clearance time for pedestrians

LD 4 too low utilization of green time for vehicles LD 5 too long red time for pedestrians

LD 6 different length of green time for opposing traffic streams LD 7 too short intergreen time

LD 8 too short green time for pedestrians

LD 9 latent dangers of refuge islands in the middle

LD 10 latent dangers at regulation “turning vehicles + pedestrians” LD 11 complex situation because of complicated and big intersections LD 12 tram station or bus stop near crosswalks

LD 13 zebra crosswalks 3.3 Traffic conflict technique (TCT) 3.3.1 Overview

“Traffic Conflict Technique (TCT)” was firstly proposed in 1966 by Hydén from Sweden and has been taken over and modified in other countries. New methods have been developed and used on estimating traffic safety especially at intersections.

The original definition of “traffic conflict” by Hydén was “an observable situation in which two or more road users approach each other in space and time to such an extent that a collision is imminent if their movements remain unchanged” and the task of TCT is to detect conflicts and scale the severity of conflicts (Hydén, 1977). TCT is thought to be able to overcome certain deficiencies in the accident based safety evaluation procedures by short time lasted and uncomplicated observation ,“three days of observations already give (normally) better estimates than waiting for three years of accident data” (Hydén, 1987).

3.3.2 Methods of pedestrian conflict observation

In this section, common methods used for pedestrian conflict observation are explained. Basically there are two types: subjective approaches and objective approaches.

Subjective approaches of TCT

Subjective approaches normally detect conflicts and scale the severity of conflicts by examining evasive actions and their impetuosity.

(1) The U.S. definition

This technique originates from a study conducted by Perkins and Harris (1968) that consisted of examining evasive actions or sudden braking. “Sudden changes in the speed movement” was used as evasive actions, for vehicles it includes braking, lane change and acceleration; for pedestrians it includes stopping, running and lateral movement to avoid conflicts.