LA GLOBALIZACIÓN COMO ENTORNO DE COMUNICACIÓN

Among a total of 46’641 crashes on Swiss motorways during six years from 2002 to 2007, there are a number of crashes used and matched with traffic data at study site. To obtain better results in later stages of the current research, every individual crash recorded at the selected study site should guarantee that: The impact of the crashes on traffic such as abnormal changes in speed or flow is observable in traffic after crash occurrences. This is essential as crash time and location are not known with precision and will be estimated based on traffic data

The crash is traffic-induced, i.e. not caused by unusual human state or technical error, etc. The specification of considered crashes is discussed in detailed in section 4.3.2.

Following sub-sections discuss about these issues.

4.3.2. Traffic‐Induced Crashes

According to FSO, (2005), faults and influences of crashes should be obtained as much as possible at the location of crashes. By observation and notice, the person who establishes the crash report can mention up to three possible faults and influences to allow identifying all the factors having played a role in the development of the crash. There are four main faults and influences for road traffic crashes:

Human influence such as the state of drivers, visibility, driving skill, attention, etc. Road and environment such as visibility, signalization, meteorological state, animals, etc. State of vehicles

Traffic and the violation of traffic rules.

In the current research, not all crashes are considered. Each crash is verified whether it will be used. For example, crashes caused by bad state of drivers (such as drunk, influenced by drugs, unqualified for driving (i.e. no driving license), etc.) are not considered. Crashes with the appearance of animals on the road are excluded. Crashes due to technical problems of vehicles are also not included. Almost all crashes due to traffic and the violation of traffic rules are included. There are nine sub-categories of causes due to traffic and violation of traffic rules. The sub-categories are:

 About speed such as speed inappropriate for traffic conditions or speed over the speed limit, etc.  About left/right movement and pre-selection such as not looking when changing lanes, quitting a

platoon while travelling closely behind another vehicle, etc.  About overtaking situation such as before or on a curve, etc.

 About overtaking decision during the traffic such as when vehicles are too close, premature return on the right lane, overtaking on the right lane, etc.

 About priority such as entering the motorway.

 About other movements in traffic such as following front vehicle too closely.

4-54

In each sub-category, there are still certain traffic violations that are not applicable for motorways such as imprudent reverse gear, not stop in front of pedestrian crossing line, etc. Crashes caused by such violation are not present in the motorway traffic crash database. There are also crashes caused by drivers when the drivers’ states were good such as overtaking on the right lane, exceeding speed limit. It is those drivers who are personally responsible for the crashes and those crashes are unconsidered.

Finally, crashes considered in the present study belong exclusively to categories D, E, and F in Table 4-1, i.e. crashes while overtaking; rear-end crashes; and crashes while changing lanes for pre-selection or bypassing, respectively. Although crashes while overtaking and crashes while changing lanes for pre- selection or bypassing are distinguishable by the aim of the movement, the development at the beginning of the crashes is more interesting for the current study. Therefore, these two crash types are called

sideswipe crashes in this dissertation. According to Figure 4-5, the rear-end and sideswipe crashes

contribute more than 41% out of all crashes on Swiss motorways during six years from 2002 to 2007.

4.3.3. Crash Observation on Traffic Data

Here, one of the main objectives is to link traffic flow conditions to crash occurrences. Therefore, it is critical that crash locations should by close to traffic detectors’ location in order that traffic evolution preceding crashes can be observed in traffic data via speed or flow changes. For this reason, crashes to be considered are limited within a buffer of one kilometer from traffic detectors (for each direction).

4.3.4. Types of Crash

When a crash occurs, the police come to the site and follow a guideline (FSO, (2005)) to determine the type of the crash. The guideline includes a series of questions whose answers are yes or no such that the crash type is determined when the answer yes is given. The questions need to be asked according to a given order. The two questions in the list are used in the example below:

Question 1: Does the crash occur between a pedestrian and a vehicle such that the driver of the vehicle

did not lose control, did not tend to avoid and did not divert his trajectory?

If the answer is yes, that is a pedestrian related crash. There are several exceptions: If there are only pedestrian involved in the crash, the crash is not traffic crash.

If that is a crash with a vehicle such that the driver lost control or tended to avoid or diverted his trajectory, that crash is classified into crash category due to slippery or loss of control.

If an animal hold by the pedestrian is wounded and the pedestrian is fine, the crash is animal-related.

Question 2: is there a frontal collision between two vehicles traveling in inversed directions?

If the answer is yes, the crash is crossing crash.

As the road is motorways, popular types of crashes include rear-end, overtaking, lane changing for pre- selection crashes (see Figure 4-5) which are of interest of the current research and single-vehicle crashes which are the most numerous. By asking and answering the series of questions, the type of crashes on motorways can be precisely determined.

4.3.5. Crash Time and Location

In Switzerland, when a crash occurs on the motorway, the police of the canton where the crash occurs are responsible for the crash report. In the survey form (FSO, 2005), there are fields to precise the crash location such as the name of the road, the direction, the kilometrical position, the geographical position, etc. However, the crash reports returned to the FSO are not completely filled in. For the study site CH023 for example, the police from Bern canton did not precise the crash locations in term of lane where the crash occurred although the GPS coordinates of the crash are available. The deviation in geographical coordinates can be as much as 3 meters and therefore, it is impossible to identify the lane where the crash occurred. In many crash cases, the traffic direction where the crashes occurred is not identifiable. It is worth noting that the geographical position of crashes is still important and accurate enough for limiting crashes in the buffer of one kilometer from traffic detectors.

As a similar issue, the crash time is not known with precision. According to FSO, (2005), if it is not possible to determine the precise time when the crash starts to occur, the person responsible for filling the survey form needs to indicate the most plausible time based on his observation.