German method for determining intergreen times 97 

According to the German method (FGSV, 1992), the intergreen time is defined as follows:

‘’The intergreen time is the interval between the end of the green time for one traffic stream and the beginning of the green time for the next one (the conflicting traffic stream)’’.

By this definition, the last vehicle of the ending green time (traffic stream A) must have cleared the conflict area at the latest when the first vehicle of the beginning green time (traffic stream B) arrives at the conflict area (see Figure 71). During the intergreen time, different movements occur: crossing and clearing movements of the last vehicle of the traffic stream A, and the entering movement of the first vehicle of the traffic stream B.

Chapter 5: Calculation of Signal Program Elements for MDCs Intergreen time

Figure 71: Clearing distance and entering distance

(Boltze, 2007 according to the German method)

All the movements occurring during the intergreen time are illustrated in Figure 72.

Figure 72: Movements of vehicles during the intergreen time

(Boltze, 2007 according to the German method)

Where: sr = clearing distance; vr = clearing speed; tr = clearance time

se = entering distance; ve = entering speed; te = entering time

sr = so + lFz ; tü = crossing time

so = basic clearing distance; tZ = intergreen time

l = fictitious length of vehicle;

conflict stream B stre am A se,B sr,A lFz s0 A s(t) t sr,A lFz se,B tZ A,B te,B tr,A tÜ conflict area

first (entering) vehicle of the beginning signal group B

last (clearing) vehicle of the ending signal group A

stop line

stop line

Chapter 5: Calculation of Signal Program Elements for MDCs Intergreen time

From the figures above, the intergreen time tZ is calculated as follows:

e r ü

Z

t

t

t

t

=

+

−

Therefore, to determine the intergreen time tZ, each term of equation (49) needs to be

determined.

a. Crossing time tü

According to RiLSA (FGSV, 2009), the crossing time is the interval between the end of the green time and the beginning of the clearance time. The clearance time is the interval needed to cover the clearing distance. The clearing distance is that distance from the stop-line to the front-top of the vehicle at the latest position that has just cleared the conflict point.

Therefore, it can also be said that the crossing time is the interval since the end of the green time until the vehicle reaches the stop-line. The crossing time exists only if the driver decides to cross the intersection at the moment of the green time ending (the amber time starts). Hereby, the crossing time is a part of the amber time, and the maximum crossing time is equal to the amber time (see Figure 73). In addition, the lower the speed limit is, the lower the clearing speed will be, and therefore the shorter the crossing time will be, because slowly driving vehicles are better able to react on the green time ending. In RiLSA 2009, tü, therefore, was set depending on the clearing

speed, for example, at 3 s for straight-on moving vehicles, and at 2 s for slowly moving vehicles (because e.g. turning vehicles normally approach the intersection at the slower speed).

Figure 73: Maximum crossing time

(Boltze, 2007 according to the German method)

b. Clearance time negative critical decision point tÜ s(t*) sH s[m] t[s] t* tG

Chapter 5: Calculation of Signal Program Elements for MDCs Intergreen time

speed vr. In terms of safety, the lower clearing speed vr is critical. According to ITE (1985), to

provide a reasonable clearance time, the use of the same value for the speed limit (vr = vzul) is not

always valid. This is especially true for protected turning movements. The preferable method for identifying the vehicle speed involves speed sampling, but estimation methods are also available. For example, ITE (1989) proposed v85 to determine the amber time, but v15 for determining the

clearance interval and assumed that v15 is 10mph (16.09 km/h) less than v85.

However, the German Guidelines for Traffic Signals (FGSV, 2009) proposed vzul = 50 km/h to

determine the amber time inside urban areas. But, to determine the clearing time, FGSV (2009) proposed the clearing speed at vr = 10 m/s (36 km/h) for straight-on vehicles, at vr = 7 m/s (25,2

km/h) for turning vehicles, and at vr = 5 m/s (18 km/h) in case the radius of the inner lane edge R

< 10 m. In other words, it may be said that for the amber time the maximum speed is critical, but for the clearing time the minimum speed is critical.

c. Entering time

According to RiLSA (FGSV, 2009), the entering time is the interval needed for the first entering vehicle to cover the entering distance se. This entering time is determined by the following

formula:

40

*

6

.

3

s

t

=

This formula is based on the assumption that the first entering vehicle is entering the stop-line at the speed of 40 km/h and keeps this speed until reaching the conflicting area; this situation has been seen as the critical case. This is quite reasonable because if it is assumed that the first vehicle is approaching the intersection at the speed of vzul = 50 km/h, this driver tends to

decelerate when approaching the red signal, but still keeps the relatively high speed. When the red-and-amber time starts and remains 1 s, the driver will accelerate again and enter the stop-line as soon as the green time begins. Therefore, the speed at the moment of entering the stop-line is usually lower than the speed limit vzul (40 km/h comparing to 50 km/h). In other words, it may be

said that the maximum entering speed is critical, but must be lower than vzul. Cases for determining the intergreen times in Germany:

Depending on the traffic situations at traffic signals in each country, the intergreen time must be considered and determined for individual cases. In Germany, the intergreen times are classified into 6 cases:

Case 1: Straight-on vehicles are clearing Case 2: Turning vehicles are clearing

Case 3: Trams are clearing without stop before the intersection

Case 4: Public transport vehicles are clearing with stop before the intersection Case 5: Cyclists are clearing

Case 6: Pedestrians are clearing

Chapter 5: Calculation of Signal Program Elements for MDCs Intergreen time