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2017 Vol.25 Issue.3,Published 2017-09-30

Articles
 
Articles
133 A modern congestion pricing policy for urban traffic:subsidy plus toll
Saeed Asadi Bagloee, Majid Sarvi
Congestion pricing is seen as an effective policy to address traffic congestion. In such policies where money, people and authorities are involved, the success generally hinges upon two factors:equity (being fair) and acceptability (to both people and authorities). The primary concern is the equity, for which "tradable credit scheme (TCS)" has been introduced and extensively studied in the literature. Nevertheless, due to the complexity of the trading schemes, the TCS has yet to find any foot in the real world. To this end, a novel idea of rewarding has substituted the trading component to be known as toll-and-subsidy scheme (TSS). The idea is to charge the drivers on some roads (toll) while rewarding them to use other alternative-and perhaps underutilized-roads (subsidy). The research of the TSS is in its infancy stage. The problem to be tackled in this study is as follows:Given a set of roads constituting a cordon line around the central business district (CBD) or across a screen line, how much toll or subsidy should be assigned to each road? The problem is first transformed into a capacitated traffic assignment problem. We employ a solution method based on augmenting the travel time of roads up to the level at which the traffic volumes do not exceed some target rates. A real dataset from the city of Winnipeg, Canada, is used as a pilot study. We then discuss policy-related applications of the TSS. It is proved in the literature that one can obtain optimal TSSs for various objectives and considerations. To this end, the non-negativity of the toll values is relaxed which results in a valid toll set. Nevertheless, the computational time is found to be of highest significance. Our method differs in the fact that the traffic volumes are bounded from the above and it is quite affordable. The main contribution is first to highlight the concept of subsidy along with traditional thought of merely toll. Second is to interpret the Lagrangian values of the capacity constraints as the values of the toll/subsidy.
2017 Vol. 25 (3): 133-149 [Abstract] ( 1855 ) [HTML 1KB] [ PDF 1413KB] ( 359 )
150 Investigation of the factors affecting the consistency of shortperiod traffic counts
Solomon Yadessa Kenno, Prasanta K. Sahu, Babak Mehran, Satish Sharma
The main intent of this study is to investigate the accuracy of short-duration traffic counts conducted during winter months. The investigation is based on 11-year sample data collected using permanent traffic counters at various locations in Alberta, Canada. Four types of road sites:commuter, regional commuter, rural long-distance, and recreational sites are studied. The sample data constitute six different durations of counts (12-, 24-, 48-, 72-, 96-h, and 1 week) taken during summer and winter months. The coefficient of variation (CV) is used as the relative measure of deviation for counts of different durations to measure the accuracy of short-period traffic counts. The study results indicate that 48-h count seems to be the most cost-effective counting interval during both summer and winter months. It is also found that the lowest values of CV result for counts taken at commuter sites, and the highest values are observed for recreational sites. Frequent changes in temperature and other weather events cause significant variation in traffic volume, which results in an increase in CV values for counts taken during winter months. The application of an adjustment factor to remove the effect of cold and snow from short-period counts is also included in this study. Introduced adjustment factors can reduce the values of CV for all counts taken during winter months. The findings of this study can lead highway agencies to improve the cost-effectiveness of their shortperiod traffic counting programs.
2017 Vol. 25 (3): 150-162 [Abstract] ( 1556 ) [HTML 1KB] [ PDF 698KB] ( 359 )
163 Modelling vehicular interactions for heterogeneous traffic flow using cellular automata with position preference
Gaurav Pandey, K. Ramachandra Rao, Dinesh Mohan
This paper proposes and validates a modified cellular automata model for determining interaction rate (i.e. number of car-following/overtaking instances) using traffic flow data measured in the field. The proposed model considers lateral position preference by each vehicle type and introduces a position preference parameter β in the model which facilitates gradual drifting towards preferred position on road, even if the gap in front is sufficient. Additionally, the model also improves upon the conventional model by calculating safe front and back gap dynamically based on speed and deceleration properties of leader and follower vehicles. Sensitivity analysis was carried out to determine the effect of β on vehicular interactions and the model was calibrated and validated using interaction rates observed in the field. Paired tests were conducted to determine the validity of the model in determining interaction rates. Results of the simulations show that there is a parabolic relationship between area occupancy and interaction rate of different vehicle types. The model performed satisfactorily as the simulated interaction rate between different vehicle types were found to be statistically similar to those observed in field. Also, as expected, the interaction rate between light motor vehicles (LMVs) and heavy motor vehicles (HMVs) were found to be higher than that between LMVs and three wheelers because LMVs and HMVs share the same lane. This could not be done using conventional CA models as lateral movement rules were dictated by only speeds and gaps. So, in conventional models, the vehicles would end up in positions which are not realistic. The position preference parameter introduced in this model motivates vehicles to stay in their preferred positions. This study demonstrates the use of interaction rate as a measure to validate microscopic traffic flow models.
2017 Vol. 25 (3): 163-177 [Abstract] ( 1343 ) [HTML 1KB] [ PDF 1356KB] ( 246 )
178 Rail fatigue crack propagation in high-speed wheel/rail rolling contact
Xiaoyu Jiang, Xiaotao Li, Xu Li, Shihao Cao
To study the wheel/rail rolling contact fatigue of high-speed trains, we obtain the distribution of contact forces between wheel and rail by introducing the strain-rate effect. Based on the finite element simulation, a two-dimensional finite element model is established, and the process of a wheel rolling over a crack is analyzed to predict the crack propagation direction. The statistics of possible crack propagation angles are calculated by the maximum circumferential stress criterion. The crack path is then obtained by using the average crack propagation angle as the crack propagation direction according to Weibull distribution. Results show that the rail crack mode of low-speed trains is different from that of high-speed trains. The rail crack propagation experiences a migration from opening mode to sliding mode under the low-speed trains; however, the rail crack mainly propagates in the opening mode under highspeed trains. Furthermore, the crack propagation rate for high-speed trains is faster than that for low-speed trains. The simulated crack paths are consistent with the experimental ones, which proves that it is reasonable to use the average value of possible crack propagation directions as the actual crack propagation direction.
2017 Vol. 25 (3): 178-184 [Abstract] ( 1435 ) [HTML 1KB] [ PDF 1940KB] ( 358 )
185 Impact of viscosity modifier on asphalt properties used for bus rapid transit lane in Chengdu
Mouhamed Bayane Bouraima, Xiao-hua Zhang, Shui-wen Zhou, Yanjun Qiu
In order to find the effect of different viscosity modifier dosages on asphalt binder's performance in bus rapid transit lanes in the city of Chengdu, three different viscosity modifiers were analyzed:TAFPACK-super (TPS), high-viscosity additive (HVA) and road-sciencetechnology (RST), and four different asphalt binders were investigated through laboratory experiments. The percentages of the viscosity modifiers used were:TPS (0%, 8%, 10%, 12%, 14% and 16%) and RST and HVA (8% and 12%) depending on the type of asphalt binder. Technical indicators of modifier asphalt were tested through conventional and unconventional binder tests. It has been found out that only a percentage greater than or equal to 14% TPS is reasonable to achieve the requirement set by 20,000 Pa s for the 60℃ dynamic viscosity on local #70 grade asphalt. The results indicate that conventional binders did not meet the requirements of the 60℃ dynamic viscosity when 12% of TPS or HVA modifiers are used. In addition, the (B-type) styrene-butadienne-styrene (SBS) modified asphalt binder has better viscosity balance than the (A-type) (SBS) modified when 8% of each of the three different kinds of viscosity modifiers is used. Therefore, the (B-type) modified SBS thus appears to be a suitable choice in asphalt mixtures for bus rapid transit lane with the 60℃ dynamic viscosity.
2017 Vol. 25 (3): 185-193 [Abstract] ( 1692 ) [HTML 1KB] [ PDF 1177KB] ( 413 )
194 Comparative analysis of cast-in-place post-tensioned and steel-concrete composite bridge bent caps
Nur Yazdani, Francisco D. B. Ruiz
The complexity of the IH-635 Managed Lanes Project, located in Dallas County, Texas, posed several technical and constructive challenges, leading to the adoption of solutions different from the traditional. Two alternative solutions for the pier cap on one of the bridge crossings over IH-35E in the IH-635 project were analyzed in this case study, a cast-in-place post-tensioned concrete cap and an innovative prefabricated steel-concrete composite cap. The approach was to use an estimation of direct costs for material and labor and consideration of construction time schedules. A supplementary numerical modeling confirmed that both alternatives behave elastically under imposed loads. The direct cost of material and labor for the two alternatives were close. However, the composite alternative required 13 days less construction time, resulting in substantial cost savings from traffic closing in the very busy traffic corridor. Traffic closing costs were substantially higher than the direct costs, especially for the post-tensioned cap. The quantification of the benefits allows more confidence in the utilization of the composites caps, leading to faster completion of bridge projects and substantial economic savings.
2017 Vol. 25 (3): 194-204 [Abstract] ( 1831 ) [HTML 1KB] [ PDF 2658KB] ( 335 )
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