Generalized Optimal Velocity Model for Traffic Flow

A generalized optimal velocity model is analyzed, where the optimal velocity function depends not only on the headway of each car but also the headway of the immediately preceding one. The stability condition of the model is derived by considering a small perturbation around the homogeneous flow solution. The effect of the generalized optimal velocity function is also confirmed with numerical simulation, by examining the hysteresis loop in the headway-velocity phase space, and the relation between flow and density of cars. In the model with a specific parameter choice, it is found that an intermediate state appears for the movement of cars, where the car keeps a certain velocity though the headway is short or long. This phenomenon is different from the ordinary stop-and-go state.Comment: 13 pages, 9 figure

Mind the Gap – Passenger Arrival Patterns in Multi-agent Simulations

In most studies mathematical models are developed finding the expected waiting time to be a function of the headway. These models have in common that the proportion of passengers that arrive randomly at a public transport stop is less as headway in-creases. Since there are several factors of influence, such as social demographic or regional aspects, the reliability of public transport service and the level of passenger information, the threshold headway for the transition from random to coordinated passenger arrivals vary from study to study. This study's objective is to investigate if an agent-based model exhibits realistic passenger arrival behavior at transit stops. This objective is approached by exploring the sensitivity of the agents' arrival behavior towards (1) the degree of learning, (2) the reliability of the experienced transit service, and (3) the service headway. The simulation experiments for a simple transit corridor indicate that the applied model is capable of representing the complex passenger arrival behavior observed in reality. (1) For higher degrees of learning, the agents tend to over-optimize, i.e. they try to obtain the latest possible departure time exact to the second. An approach is presented which increases the diversity in the agents' travel alternatives and results in a more realistic behavior. (2) For a less reliable service the agents' time adaptation changes in that a buffer time is added between their arrival at the stop and the actual departure of the vehicle. (3) For the modification of the headway the simulation outcome is consistent with the literature on arrival patterns. Smaller headways yield a more equally distributed arrival pattern whereas larger headways result in more coordinated arrival patterns

Maximin Headway Control of Automated Vehicles for System Optimal Dynamic Traffic Assignment in General Networks

This study develops the headway control framework in a fully automated road network, as we believe headway of Automated Vehicles (AVs) is another influencing factor to traffic dynamics in addition to conventional vehicle behaviors (e.g. route and departure time choices). Specifically, we aim to search for the optimal time headway between AVs on each link that achieves the network-wide system optimal dynamic traffic assignment (SO-DTA). To this end, the headway-dependent fundamental diagram (HFD) and headway-dependent double queue model (HDQ) are developed to model the effect of dynamic headway on roads, and a dynamic network model is built. It is rigorously proved that the minimum headway could always achieve SO-DTA, yet the optimal headway is non-unique. Motivated by these two findings, this study defines a novel concept of maximin headway, which is the largest headway that still achieves SO-DTA in the network. Mathematical properties regarding maximin headway are analyzed and an efficient solution algorithm is developed. Numerical experiments on both a small and large network verify the effectiveness of the maximin headway control framework as well as the properties of maximin headway. This study sheds light on deriving the desired solution among the non-unique solutions in SO-DTA and provides implications regarding the safety margin of AVs under SO-DTA

Public transport values of time

OBJECTIVES The objectives of this aspect of the study are to provide recommended valuations of: • Public transport in-vehicle time (IVT) • Walk time • Wait time/headway with appropriate modifiers according to key factors such as: • Mode user type • The mode to which the value relates • Journey distance and inter urban or urban context • Journey purpose A recommended procedure for updating values of time over time is also required. Although this issue is touched upon in this paper, a more detailed analysis is the subject of a separate aspect of the study and is reported in Working Paper 566. The Accent and Hague Consulting Group study did not cover public transport. Nor is this study conducting fresh empirical research. We must therefore base our recommendations on other existing studies. Fortunately, there is a wealth of British evidence on the value of time. Section 2 provides some background to the valuations of time for public transport users and the valuation of attributes which are important aspects of public transport use. Section 3 details the additional data that has been collected to enhance our previous data sets upon which we have conducted meta-analysis (Wardman, 2001) whilst Section 4 presents tabulations of the money values of time, and the time values of walk, wait and headway, disaggregated as far as is sensible by purpose, mode and whether the journey is urban or inter-urban. Section 5 describes the principal approach that we have adopted to explain the values of time obtained from the many different studies that are available to us. Section 6 is concerned with a regression model estimated to the money values for all travellers. From this model are extracted the money values of time and the IVT equivalent values of walk time, wait time and headway for public transport users. The IVT values can be expressed as absolute values or as relative to car users’ values. The latter is useful where recommended public transport values are derived as a series of modifiers to car users’ values. As a check of the IVT values of walk, wait and headway implied by the model estimated to money values, we report in section 7 a model estimated solely to the IVT values of walk, wait and headway. Concluding remarks are provided in section 8. Recommendations and comparisons with other aspects of the study are a feature of Working Paper 567

AMTV headway sensor and safety design

A headway sensing system for an automated mixed traffic vehicle (AMTV) employing an array of optical proximity sensor elements is described, and its performance is presented in terms of object detection profiles. The problem of sensing in turns is explored experimentally and requirements for future turn sensors are discussed. A recommended headway sensor configuration, employing multiple source elements in the focal plane of one lens operating together with a similar detector unit, is described. Alternative concepts including laser radar, ultrasonic sensing, imaging techniques, and radar are compared to the present proximity sensor approach. Design concepts for an AMTV body which will minimize the probability of injury to pedestrians or passengers in the event of a collision are presented

Investigating the Embodied Effect in Drivers’ Safe Headway Learning

abstract: Safe headway learning plays a core role in driving education. Traditional safe headway education just use the oral and literal methods to educate drivers the concept of safe headway time, while with the limitation of combining drivers subject and situational domains for drivers to learn. This study investigated that whether using ego-moving metaphor to embody driver's self-awareness can help to solve this problem. This study used multiple treatments (ego-moving and time-moving instruction of safe time headway) and controls with pretest experimental design to investigate the embody self-awareness effect in a car-following task. Drivers (N=40) were asked to follow a lead car at a 2-seconds safe time headway. Results found that using embodied-based instructions in safe headway learning can help to improve driver's headway time accuracy and performance stability in the car-following task, which supports the hypothesis that using embodied-based instructions help to facilitate safe headway learning. However, there are still some issues needed to be solved using embodied-based instructions for the drivers' safe headway education. This study serves as a new method for the safe headway education while providing empirical evidence for the embodied theories and their applications.Dissertation/ThesisMasters Thesis Applied Psychology 201