Examining the effect of speed,roadside features,and roadway geometry on crash experience along a rural corridor

This paper presents a current investigation into crash experience along a 15.7-mile rural corridor in southwest Montana with the aim of better understanding crash causal factors along the corridor. The study utilized ten years of crash data, geometric data, and observed freeflow speed data along the corridor. A systematic approach was used where every tenth of a mile was described in term of the crash experience, speed, alignment, and roadside features. Using bivariate and multivariate statistical anal-yses, the study investigated the crash experience along the corridor as well as some of the underlying relationships which could explain some of the crash causal factors. Results show a strong association between crash rates and horizontal curvatures even for flat curves that can be negotiated at speeds above the posted speed limit, per the highway design equations. Higher crash rates were also found to be associated with the difference between the observed free-flow speeds and the speed dictated by the curve radius or sight distance as per the design equations. Further, results strongly support the safety benefits of guardrails as evidenced by the lower crash rates and severities. The presence of fixed objects and the steepness of side slopes were also found to have an effect on crash rates and severities.     

Modal split models based on car availability: the application of such models in studies of medium sized towns

This paper discusses the need for a new approach to urban transportation modelling in recognition that at least in medium sized towns the choice of model is largely dominated by car availability.     

Bond Graphs, Normal Modes and Vehicular Structures

Bond graph modeling techniques are used to represent the normal mode dynamic behavior of uniform Bernoulli-Euler beams. The independent beam models are then coupled together to form a distributed system structure of arbitrary complexity. The resulting overall system bond graph is shown to yield the governing state equations in a straightforward manner. Then, through proper ordering of the equations, the normal modes and frequencies of the coupled system are easily obtained

This procedure is demonstrated for a vehicle A-frame structure. In addition, the bond graph model is modified to include primary and secondary suspension dynamics.     

Unlimited Access

Universities and public transit agencies have together invented an arrangement – called Unlimited Access – that provides fare-free transit service for over 825,000 people. The university typically pays the transit agency an annual lump sum based on expected student ridership, and students simply show their university identification to board the bus. This paper reports the results of a survey of Unlimited Access programs at 35 universities. University officials report that Unlimited Access reduces parking demand, increases students' access to the campus, helps to recruit and retain students, and reduces the cost of attending college. Transit agencies report that Unlimited Access increases ridership, fills empty seats, improves transit service, and reduces the operating cost per rider. Increases in student transit ridership ranged from 71 percent to 200 percent during the first year of Unlimited Access, and growth in subsequent years ranged from 2 percent to 10 percent per year. The universities' average cost for Unlimited Access is $30 per student per year.     

汽车面漆的加速酸蚀研究

为建立新的汽车酸蚀试验方法开展了一系列的研究工作,测试了酸雨的组成和pH值,统计了降雨频率和持续时间、空气和样品温度等大量的环境参数,确认pH值、温度、湿度、紫外光谱、样品的辐照量以及样品的放置角度等关键测试参数。通过对这些环境参数的记录分析,研制出一种仿酸雨溶液和一个加速测试程序,并对一款加速老化试验装置进行了改进,使其能极好地模仿户外的酸蚀结果。     

停车收费合理定价--基于需求的旧金山停车定价模式评价

除少数能够找到便宜停车位的幸运驾驶人外,价格过低和过度拥挤的路内停车位给每个人都制造了难题;其他所有为寻找可用停车位而巡游的驾驶人因此浪费了时间和燃料,导致交通拥堵并且污染空气。价格过高和占用率过低的路内停车位同样存在问题,当路内停车位闲置时,商家失去潜在的顾客,员工失去工作,而城市失去税收。为了解决这些问题,旧金山启动了SFpark项目,通过价格调整实现每个街区有1~2个可用停车位的目标。为了衡量价格如何影响路内停车位占用率,根据项目第一年内超过5000次价格和占用率变动数据计算价格需求弹性。价格需求弹性的平均值为-0.4,但是随时间、地点及其他因素大幅变化。在第一年内平均停车价格下降1%,因此,SFpark调整了停车价格但总体上并未涨价。首次使用测量出的占用率估计路内停车的需求弹性,同时也首次评价随时间和地点而变化的定价模式以用于路内停车管理。指出旧金山可以通过增加驾驶人对变动停车价格的意识,减少残疾标志的滥用以及引入季节性价格调整来改进该项目。其他城市可吸纳绩效停车定价作为拥挤收费的一种形式。     

Minimizing the Path Radius of Curvature for Collision Avoidance

When a driver is suddenly presented with an obstacle in his path, or realizes that his speed is too great for the curved road ahead, commonly he saturates both inputs of steering and braking and thereby jeopardizes his chances of successfully avoiding a collision or negotiating the turn. Although anti-lock braking systems (ABS) avoid saturation of the braking and steerability usually remains, there is evidence to suggest that the vehicle performance with this system could be greatly improved. Could the steering, in addition to the braking, be automatically controlled to improve the performance? Because these threatening situations are so variable, it is very difficult to find a controller which can override both driver inputs and is always beneficial. Using a very simple model of the vehicle, the concept of minimizing the average radius of curvature of the path through controlling both driver inputs is shown to always be beneficial, and worthwhile. The results also carry over to a more realistic model.     

Total factor productivity growth in Australian national railways — An application of shadow prices

The usual formulation of total factor productivity (TFP) growth is generalised to a multi-output, multi-input production process. The general expression derived makes no assumption about the objective of the firm, nor about the relationship between prices and associated marginal values. It can therefore accommodate, in addition to various firm objectives, the introduction of shadow pricing into the measurement of productivity growth. The theory is applied to the case of the Australian National Railways Commission (AN Rail), where excess staff levels, and the delivery of certain ‘community service obligations’ provide examples of the application of shadow prices. Rates of TFP growth are calculated by applying both the traditional formulation and the more general one accommodating any divergence between actual and shadow prices. When shadow pricing is accounted for, the average compound rate of TFP growth in AN Rail falls by up to 37%.     

Semi-Active Heave and Pitch Control for Ground Vehicles

A model is presented which includes both the heave and pitch motions of a vehicle traversing a roadway. Provision is made for testing totally passive, totally active, and semi-active secondary suspensions. Control strategies are developed for the totally active case and vehicle isolation is demonstrated. These active controllers are then modified to be semi-active, i.e., no power is provided from the controller to the vehicle. The semi-active isolation is shown to be comparable to the totally active system and much superior to the passive suspension.