Long T. Truong

Who’s calling? Social networks and mobile phone use among motorcyclists

Mobile phone use while riding a motorcycle poses a key safety risk, particularly among younger people who have been found to be more susceptible to distracted driving. While previous research has examined the influence of social networks on mobile phone use while driving a car, no research has explored this association in the context of motorcycle use. Using a survey of university students in Vietnam, this research explores the association between social networks and mobile phone use among motorcyclists and the links this has to reported crashes/falls. Results show that the majority of students are most likely to use a mobile phone to communicate with a friend while riding, either through talking (56.5%) or text messaging (62.0%). However, respondents who frequently talk to a girlfriend/boyfriend or spouse while riding were more likely to experience a crash/fall than those who frequently talk with others while riding (e.g. parent, brother/sister). In addition, those who frequently text message a friend while riding were more likely to experience a crash/fall than those who frequently text message others while riding. The results highlight a clear association between social networks and mobile phone use while riding a motorcycle. Developing a culture of societal norms, where mobile phone use while riding a motorcycle is considered socially unacceptable, will help to reduce the prevalence and ultimate crash risk associated with mobile phone use while riding.

Studying the Safety Impact of Autonomous Vehicles Using Simulation-Based Surrogate Safety Measures

Autonomous vehicle (AV) technology has advanced rapidly in recent years with some automated features already available in vehicles on the market. AVs are expected to reduce traffic crashes as the majority of crashes are related to driver errors, fatigue, alcohol, or drugs. However, very little research has been conducted to estimate the safety impact of AVs. This paper aims to investigate the safety impacts of AVs using a simulation-based surrogate safety measure approach. To this end, safety impacts are explored through the number of conflicts extracted from the VISSIM traffic microsimulator using the Surrogate Safety Assessment Model (SSAM). Behaviours of human-driven vehicles (HVs) and AVs (level 4 automation) are modelled within the VISSIM’s car-following model. The safety investigation is conducted for two case studies, that is, a signalised intersection and a roundabout, under various AV penetration rates. Results suggest that AVs improve safety significantly with high penetration rates, even when they travel with shorter headways to improve road capacity and reduce delay. For the signalised intersection, AVs reduce the number of conflicts by 20% to 65% with the AV penetration rates of between 50% and 100% (statistically significant at ). For the roundabout, the number of conflicts is reduced by 29% to 64% with the 100% AV penetration rate (statistically significant at ).

Does combining transit signal priority with dedicated bus lanes or queue jump lanes at multiple intersections create multiplier effects

An extensive body of literature deals with the design and operation of public transport (PT) priority measures. However, there is a need to understand whether providing transit signal priority with dedicated bus lanes (TSPwDBL) or transit signal priority with queue jump lanes (TSPwQJL) at multiple intersections creates a multiplier effect on PT benefits. If the benefit from providing priority together at multiple intersections is greater than the sum of benefits from providing priority separately at each of those individual intersections, a multiplier effect exists. This paper explores the effects of providing TSPwDBL or TSPwQJL at multiple intersections on bus delay savings and person delay savings. Simulation results reveal that providing TSPwDBL or TSPwQJL at multiple intersections may create a multiplier effect on one-directional bus delay savings, particularly when signal offsets provide bus progression for that direction. The multiplier effect may result in a 5% to 8% increase in bus delay savings for each additional intersection with TSPwDBL or TSPwQJL. A possible explanation is that TSPwDBL and TSPwQJL can reduce the variations in bus travel times and thus allow signal offsets—which account for bus progression—to perform even better. Furthermore, results show little evidence of the existence of a multiplier effect on person delay savings, particularly for TSPwQJL with offsets that favor person delay savings. A policy implication of these findings is that considerable PT benefits can be achieved by providing both time and space priority in combination on a corridorwide scale.

A meta-analysis and synthesis of public transport customer amenity valuation research

ABSTRACT This paper synthesises published research concerned with the valuation of public transport customer amenities. It includes normalisation of published values to equivalent terms, a meta-analysis of factors influencing these values, a review of valuation methods and issues faced in applying these methods, and an identification of gaps in knowledge. Some 57 separate research publications in this area were identified. Valuation methods adopted included stated preference, revealed preference, customer ratings, priority evaluator, maximum difference scaling and benefit/value transfer. Of these, stated preference was the most common published approach, however in practice benefit/value transfer is the most common method to apply values in project appraisal. Key issues associated with valuation include substantial variation in values (which are often context dependant) and the adoption of different units for expressing values, thereby limiting their transferability. Some 556 separate customer amenity values were identified relating to 97 separate amenity types. Almost all valuations were below 2 minutes of equivalent in-vehicle travel time value. Meta-analysis identified five types of significant predictors of values (R2 = 0.23): study location (Scandinavia), valuation method (stated preference), mode (train/metro), amenity group (access) and journey stage (boarding/alighting). Future research needs to disaggregate valuations by market segment.

Analytical Approach to Estimate Delay Reduction Associated with Bus Priority Measures

Bus delay reduction is an essential input to the objective evaluation of the performance of Public Transport Priority (PTP) measures. Functions for estimating bus delay reduction associated with various types of PTP measures can be used to optimise priority and signal control, or used as a planning tool when more expensive simulation is not available. However, existing delay functions for evaluating PTP measures, such as Dedicated Bus Lanes (DBLs) or Transit Signal Priority (TSP), tend to ignore delay associated with bus acceleration. Moreover, there is no study dedicated to developing bus delay functions to evaluate the performance of Queue Jump Lanes (QJLs) or QJLs combined with TSP. This paper proposes delay functions to analytically estimate bus delay effects for a range of PTP measures, including DBLs, QJLs, TSP, TSP combined with QJLs, and TSP combined with DBLs. Kinematic Wave Theory (KWT) is used to estimate queuing delays at traffic signals. Delay associated with bus acceleration is also analytically approximated. The proposed bus delay functions are validated using traffic micro-simulation, which indicates that the proposed functions accurately estimate bus delay effects of the considered PTP measures with small errors.

How Many Simulation Runs are Required to Achieve Statistically Confident Results: A Case Study of Simulation-Based Surrogate Safety Measures

This research explores how to compute the minimum number of runs (MNR) required to achieve a specified confidence level for multiple measures of performance (MOP) of a simulated traffic network. Traditional methods to calculate MNR consider the confidence intervals of multiple MOPs separately and hence are not able to control the overall confidence level. A new method to calculate MNR is proposed, which sequentially runs the model and recalculates sample standard deviations and means whenever an additional run is made until a stopping condition based on the Bonferroni inequality is satisfied. The overall confidence level is controlled by the Bonferroni inequality. The proposed method is computationally practical since it can be implemented automatically in most traffic micro-simulation packages. The proposed method is evaluated using a case study with multiple simulation-based surrogate safety measures, including time to collision (TTC) or deceleration rate required to avoid a crash (DRAC), and an empirical confidence level analysis based on a very large number of runs. Evaluation results indicate the effectiveness of the proposed method as it enables all MOPs at the same time to be estimated accurately at the desired confidence level whereas traditional methods do not. In addition, the proposed method is not conservative since it does not require significantly more runs compared to traditional methods.