In order to improve the performance of the signalized intersection,an unconventional scheme tandem design(TD)is proposed.A simulation experiment is conducted to evaluate the capacity and delay under the unconventional...In order to improve the performance of the signalized intersection,an unconventional scheme tandem design(TD)is proposed.A simulation experiment is conducted to evaluate the capacity and delay under the unconventional scheme and two conventional lane assignment schemes.First,the VISSIM is employed as microsimulation to obtain the delay of different designs at signalized T-intersections under different conditions of traffic flow and turning proportion.Secondly,a method based on discriminant analysis(DA)is proposed to determine the best design scheme using the flow and turning proportion as inputs.Finally,a case study in Changsha city,China is used to demonstrate the efficiency and accuracy of these findings.The results indicate that the traffic flow and turning proportion are the crucial factors in scheme selection of lane assignment.Different from the previous research,the TD has better performance over various traffic flow levels.Furthermore,a proper proportion of left turns makes TD an outstanding option,which can reduce the delay and decrease the average number of stops and queue length significantly.However,the proportion should not be too high or too low.The research results can help practitioners obtain a quantitative view of appropriate design schemes at signalized intersections when trying to relieve traffic congestion according to different traffic conditions.展开更多
The most common type of intersection improvement considered in Ghana is signalization. However, other actions such as the installation of left-turn lanes have been proven to improve the efficiency and safety of an int...The most common type of intersection improvement considered in Ghana is signalization. However, other actions such as the installation of left-turn lanes have been proven to improve the efficiency and safety of an intersection without the need for signalization in the short term. Warrants which guide the installation of such lanes in Ghana are adopted from elsewhere and as a result do not reflect local traffic flow conditions. This study established volume warrants based on a delay threshold to guide the installation of left- turn lanes at unsignalized T-intersections using VISSIM micro simulation tool. The VISSIM model was calibrated using traffic flow, delay, average and maximum queue length data obtained from a two-hour video recording of the case study intersection during the morning peak period. After calibration, several scenarios covering a wide range of opera- tional conditions were simulated. Using level of service （LOS） C cut off point of 25 s/veh as the maximum acceptable delay to minor road left-turning traffic, an equation y = -0.57x ＋1091 has been developed which predicts the minor road left-turn volume threshold （y） above which a minor road left-turn lane may be considered and below which a minor road left-turn lane may not be necessary for a range of major road volumes （x）. The critical delay to major road left-turning traffic was found to be 16 s/veh. Major road left-turn lane volume warrants were also determined based on this threshold delay value. The approach used in this study can serve as a guide that can be used by metropolitan and municipal road en- gineers to assess the need for left-turn lanes.展开更多
Traffic safety and performance measures such as crash risk and queue lengths or travel times are influenced by several important factors including those related to environment,human,and roadway design,especially at in...Traffic safety and performance measures such as crash risk and queue lengths or travel times are influenced by several important factors including those related to environment,human,and roadway design,especially at intersections.Previous research has studied different aspects related to these factors,yet these characteristics are not fully investigated with a focus on age and experience of drivers.In this paper,we investigate this issue by using a two-phase approach via a case study application on a critical T-intersection in the City of Tallahassee,Florida.The first phase includes a scenario-based microsimulation analysis through the use of a microscopic simulation software,namely VISSIM,to illustrate the variations in traffic performance measures with respect to driver compositions of different age groups in the traffic stream.A variety of scenarios is created where the driving characteristics are provided as inputs to these scenarios in terms of decision making and risk taking.This is also supported by a sensitivity analysis conducted based on the driver composition in the traffic.The second phase includes the analysis of microsimulation outputs via a tool developed by Federal Highway Administration tool,namely the Surrogate Safety Assessment Model(SSAM),in order to determine the traffic conflicts that occur in each scenario.These conflicts are also compared with real-life crash data for validation purposes.Results show that(a) the differences in risk perception that affect driving behavior might be significant in influencing traffic safety and performance measures,and(b) the proposed approach is considerably successful in simulating the actual crash conflict points.展开更多
An offset T-intersection splits a conventional four leg intersection into two three-leg T-intersections to reduce the number of conflicts. While the safety benefits of offset T-intersections have been widely documente...An offset T-intersection splits a conventional four leg intersection into two three-leg T-intersections to reduce the number of conflicts. While the safety benefits of offset T-intersections have been widely documented, the effects on operations are not well understood. To fix that, this paper employed microsimulation modeling to investigate the differences in operational performance between offset T-intersections and four-leg standard intersections under various traffic demands, intersection spacings, and signal timing schemes for three development types: superstore, hybrid gas station, and residential area. Queue length and delay were employed as measurements of effectiveness. Based on microsimulation modeling, we found that under most of the tested scenarios, offset T-intersections were superior to four-leg intersections in terms of reducing delay for the main street traffic. In addition, we found that the left–right (L-R) offset T-intersection configuration outperformed the right-left (R-L) offset configuration in terms of preventing main-street left turn queue spillback. Based on the simulation results, the paper provided practice-ready guidelines on selecting an optimum intersection configuration for each specific development type given the volume demands and known geometric constraints for a given site.展开更多
Let n, s1,s2, and sn be positive integers. Assume M(s1 s2,,sn)={(x1,x2,... ,xn)|0≤xi≤si, xi is an integer for each i}.For a=(a1,a2,....,an)∈M(s1,s2,...,sn.),M(s1,s2,....,sn.), and A{1,2,..,n}, denote sp(a)={j |1≤ ...Let n, s1,s2, and sn be positive integers. Assume M(s1 s2,,sn)={(x1,x2,... ,xn)|0≤xi≤si, xi is an integer for each i}.For a=(a1,a2,....,an)∈M(s1,s2,...,sn.),M(s1,s2,....,sn.), and A{1,2,..,n}, denote sp(a)={j |1≤ j≤n, aj≥p}, Sp(r)={sp(a) |aam}, and WP(A)=P(si-p).Fis called an I-intersecting family if, for any a,6eF, a.Abi=min(ai,6i)>p for at least t i'8. F iscalled a greedy Ir-illtersecting flaily if F is an Ir-intersecting family and WP(A)ZWr(B+A') forany ASp and any BOA with B=t-1.In this paper, we obtain a sharp upper bound of for greedy Ir-intersecting families inM(sl,s2Z,'',sn.) for the case 2p5B' (IBIds) and 81 >BZ >...>B..展开更多
Left turn traffic at unsignalized T-intersection on undivided rural two-lane high-speed highways poses both operational and safety challenges.More complexities are faced by through drivers in the same direction as the...Left turn traffic at unsignalized T-intersection on undivided rural two-lane high-speed highways poses both operational and safety challenges.More complexities are faced by through drivers in the same direction as the stopped or slowed down left-turn vehicle must choose to either slow down and wait or bypass the left-turn vehicle.Therefore,this study intends to explore the operational characteristics of these facilities.The focus is on the reaction of the drivers behind the left-turn vehicle in terms of the types of maneuvers taken to avoid collision and the distance upstream for the evasive maneuvers using field observations.Further,the impact of the drivers’reaction on the intersection delay is assessed using a simulation analysis of 17 generic 10.5-mile two-lane corridors with varying configurations of passing lanes at or near the intersection with and without a left-turn lane.The field observation findings from five sites reveal that drivers will move to the shoulder to avoid slowing and stopping or colliding with the left-turn vehicle.The distance at which drivers move to the shoulder differs for the sites studied.The simulation results show that a relatively similar magnitude of reduction in intersection delay could be achieved by addition of either passing lane or left-turn lane,such addition is beneficial for at least 17000 vpd intersection volume where the passing lane does not end within 1500 ft is downstream of the intersection.The findings are expected to improve traffic operations at T-intersections on rural two-lane highways.展开更多
Two families F and G of k-subsets of {1, 2,..., n} are called non-trivial cross t-intersecting if|F ∩ G|≥t for all F ∈ F, G ∈ G and | ∩ {F : F ∈ F}| < t, | ∩ {G : G ∈ G}| < t. In the present paper,we det...Two families F and G of k-subsets of {1, 2,..., n} are called non-trivial cross t-intersecting if|F ∩ G|≥t for all F ∈ F, G ∈ G and | ∩ {F : F ∈ F}| < t, | ∩ {G : G ∈ G}| < t. In the present paper,we determine the maximum product of the sizes of two non-trivial cross t-intersecting families of k-subsets of{1, 2,..., n} for n≥4(t + 2)2k2, k≥5, which is a product version of the Hilton-Milner-Frankl theorem.展开更多
文摘In order to improve the performance of the signalized intersection,an unconventional scheme tandem design(TD)is proposed.A simulation experiment is conducted to evaluate the capacity and delay under the unconventional scheme and two conventional lane assignment schemes.First,the VISSIM is employed as microsimulation to obtain the delay of different designs at signalized T-intersections under different conditions of traffic flow and turning proportion.Secondly,a method based on discriminant analysis(DA)is proposed to determine the best design scheme using the flow and turning proportion as inputs.Finally,a case study in Changsha city,China is used to demonstrate the efficiency and accuracy of these findings.The results indicate that the traffic flow and turning proportion are the crucial factors in scheme selection of lane assignment.Different from the previous research,the TD has better performance over various traffic flow levels.Furthermore,a proper proportion of left turns makes TD an outstanding option,which can reduce the delay and decrease the average number of stops and queue length significantly.However,the proportion should not be too high or too low.The research results can help practitioners obtain a quantitative view of appropriate design schemes at signalized intersections when trying to relieve traffic congestion according to different traffic conditions.
文摘The most common type of intersection improvement considered in Ghana is signalization. However, other actions such as the installation of left-turn lanes have been proven to improve the efficiency and safety of an intersection without the need for signalization in the short term. Warrants which guide the installation of such lanes in Ghana are adopted from elsewhere and as a result do not reflect local traffic flow conditions. This study established volume warrants based on a delay threshold to guide the installation of left- turn lanes at unsignalized T-intersections using VISSIM micro simulation tool. The VISSIM model was calibrated using traffic flow, delay, average and maximum queue length data obtained from a two-hour video recording of the case study intersection during the morning peak period. After calibration, several scenarios covering a wide range of opera- tional conditions were simulated. Using level of service （LOS） C cut off point of 25 s/veh as the maximum acceptable delay to minor road left-turning traffic, an equation y = -0.57x ＋1091 has been developed which predicts the minor road left-turn volume threshold （y） above which a minor road left-turn lane may be considered and below which a minor road left-turn lane may not be necessary for a range of major road volumes （x）. The critical delay to major road left-turning traffic was found to be 16 s/veh. Major road left-turn lane volume warrants were also determined based on this threshold delay value. The approach used in this study can serve as a guide that can be used by metropolitan and municipal road en- gineers to assess the need for left-turn lanes.
基金supported by United States Department of Transportation grant DTRT13-G-UTC42
文摘Traffic safety and performance measures such as crash risk and queue lengths or travel times are influenced by several important factors including those related to environment,human,and roadway design,especially at intersections.Previous research has studied different aspects related to these factors,yet these characteristics are not fully investigated with a focus on age and experience of drivers.In this paper,we investigate this issue by using a two-phase approach via a case study application on a critical T-intersection in the City of Tallahassee,Florida.The first phase includes a scenario-based microsimulation analysis through the use of a microscopic simulation software,namely VISSIM,to illustrate the variations in traffic performance measures with respect to driver compositions of different age groups in the traffic stream.A variety of scenarios is created where the driving characteristics are provided as inputs to these scenarios in terms of decision making and risk taking.This is also supported by a sensitivity analysis conducted based on the driver composition in the traffic.The second phase includes the analysis of microsimulation outputs via a tool developed by Federal Highway Administration tool,namely the Surrogate Safety Assessment Model(SSAM),in order to determine the traffic conflicts that occur in each scenario.These conflicts are also compared with real-life crash data for validation purposes.Results show that(a) the differences in risk perception that affect driving behavior might be significant in influencing traffic safety and performance measures,and(b) the proposed approach is considerably successful in simulating the actual crash conflict points.
文摘An offset T-intersection splits a conventional four leg intersection into two three-leg T-intersections to reduce the number of conflicts. While the safety benefits of offset T-intersections have been widely documented, the effects on operations are not well understood. To fix that, this paper employed microsimulation modeling to investigate the differences in operational performance between offset T-intersections and four-leg standard intersections under various traffic demands, intersection spacings, and signal timing schemes for three development types: superstore, hybrid gas station, and residential area. Queue length and delay were employed as measurements of effectiveness. Based on microsimulation modeling, we found that under most of the tested scenarios, offset T-intersections were superior to four-leg intersections in terms of reducing delay for the main street traffic. In addition, we found that the left–right (L-R) offset T-intersection configuration outperformed the right-left (R-L) offset configuration in terms of preventing main-street left turn queue spillback. Based on the simulation results, the paper provided practice-ready guidelines on selecting an optimum intersection configuration for each specific development type given the volume demands and known geometric constraints for a given site.
文摘Let n, s1,s2, and sn be positive integers. Assume M(s1 s2,,sn)={(x1,x2,... ,xn)|0≤xi≤si, xi is an integer for each i}.For a=(a1,a2,....,an)∈M(s1,s2,...,sn.),M(s1,s2,....,sn.), and A{1,2,..,n}, denote sp(a)={j |1≤ j≤n, aj≥p}, Sp(r)={sp(a) |aam}, and WP(A)=P(si-p).Fis called an I-intersecting family if, for any a,6eF, a.Abi=min(ai,6i)>p for at least t i'8. F iscalled a greedy Ir-illtersecting flaily if F is an Ir-intersecting family and WP(A)ZWr(B+A') forany ASp and any BOA with B=t-1.In this paper, we obtain a sharp upper bound of for greedy Ir-intersecting families inM(sl,s2Z,'',sn.) for the case 2p5B' (IBIds) and 81 >BZ >...>B..
文摘Left turn traffic at unsignalized T-intersection on undivided rural two-lane high-speed highways poses both operational and safety challenges.More complexities are faced by through drivers in the same direction as the stopped or slowed down left-turn vehicle must choose to either slow down and wait or bypass the left-turn vehicle.Therefore,this study intends to explore the operational characteristics of these facilities.The focus is on the reaction of the drivers behind the left-turn vehicle in terms of the types of maneuvers taken to avoid collision and the distance upstream for the evasive maneuvers using field observations.Further,the impact of the drivers’reaction on the intersection delay is assessed using a simulation analysis of 17 generic 10.5-mile two-lane corridors with varying configurations of passing lanes at or near the intersection with and without a left-turn lane.The field observation findings from five sites reveal that drivers will move to the shoulder to avoid slowing and stopping or colliding with the left-turn vehicle.The distance at which drivers move to the shoulder differs for the sites studied.The simulation results show that a relatively similar magnitude of reduction in intersection delay could be achieved by addition of either passing lane or left-turn lane,such addition is beneficial for at least 17000 vpd intersection volume where the passing lane does not end within 1500 ft is downstream of the intersection.The findings are expected to improve traffic operations at T-intersections on rural two-lane highways.
基金supported by National Natural Science Foundation of China (Grant No. 11701407)
文摘Two families F and G of k-subsets of {1, 2,..., n} are called non-trivial cross t-intersecting if|F ∩ G|≥t for all F ∈ F, G ∈ G and | ∩ {F : F ∈ F}| < t, | ∩ {G : G ∈ G}| < t. In the present paper,we determine the maximum product of the sizes of two non-trivial cross t-intersecting families of k-subsets of{1, 2,..., n} for n≥4(t + 2)2k2, k≥5, which is a product version of the Hilton-Milner-Frankl theorem.
