VSS 9 2015

Delays On the basis of the collected data, delays that the presence of a bus causes general traffic were examined. They were calculated by subtracting the free flow travel time from the actual travel time. As explained, the flow at C2 is distorted by a traffic light. By just comparing the actual departure times at C2 to the arrival times at C1, huge delays which include waiting times during the red time of the signal will result. In comparison, delays due to the presence of a bus could be minor and hardly detectable. Consequently, the already introduced concept of virtual departure times was deployed. The analyzed values were named “delay differences” and were calculated by sub- tracting the virtual departure times from the actual departure times at C2. Several effects, such as deceleration on account of the following right-turn, influence the delay difference. It was impossible to quantify each effect separately, but by comparing the delay difference of vehicles influenced by the bus to the ones that do not come into contact with a bus, the impact of a bus’ presence could be examined, which was actually of interest. The distribution shows that the delay differences are gener- ally higher under the influence of a bus. The investigation further unveiled that cars flowing behind the bus experi- enced the largest delays, namely almost double the amount compared to vehicles outside of bus influence, whereas cars driving ahead of a bus suffered practically no additional de- lays. At first, the overall resulting delay augmentation may seem minor, since it is just around 1 s. But these delays occur in the short distance of 42 m between C1 and C2 and are thus caused by a speed reduction by about 11% on average. Vehicles driving behind a bus even suffered a travel time increase of 25% compared to cars flowing in the absence of a bus, which corresponds to a speed reduction of 20%. Capacity A particularly interesting analysis is the impact of a bus’ presence on traffic flow. The capacities at C1 were calculated separately for all ve- hicles passing the bus during its halt at the bus stop. The resulting capacity was no smaller than when there was no bus present. It could thus be concluded that buses driving in their own reserved lane do not exert any influence on cars on the remaining lanes. Given this insensitivity, the observed capacity at C1 (2370 veh/h) could be assumed to be the road’s general capacity per lane and was set as reference flow. The influence of the right hand bend on capacity had to be taken in consideration (by dividing the reference flow by 4 | Comparison of capacity values. 4 | Comparaison des valeurs de capacité. 4 | Vergleich der Belastbarkeitswerte. 3 | Histogram of delay differences at C2. 3 | Histogramme des différences de retard en C2. 3 | Histogramm der Verzögerungsunterschiede an der Stelle C2. FACHARTIKEL | ARTICLES TECHNIQUES30 STRASSEUNDVERKEHRNR.9,SEPTEMBER2015 ROUTEETTRAFICNo 9,SEPTEMBRE2015 VSS_SV_09_2015.pdf 30VSS_SV_09_2015.pdf 30 28.09.15 10:4028.09.15 10:40 VSS_SV_09_2015.pdf 30VSS_SV_09_2015.pdf 3028.09.1510:4028.09.1510:40

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