行驶质量评价指标的回顾和展望

道路作为满足公众行驶需要的一种特殊产品,其好坏的根本量度之一就是行驶质量评价指标。由于这个指标取决于道路的破损情况,因此将其与道路表面的粗糙度特征建立回归关系才方便应用。自从20世纪60年代以来,确定行驶质量指标的主要参数就不断演变。先是人工实测车辙,破损及修补面积,再是各种仪器实测的路面平整度,比如国际平整度指数,IRI。本文在大量的研究基础上,指出了现行主要参数的不足,并提出了一个确定行驶质量指标的新参数,既乘客所直接感受到的竖直方向上的加速度的变化率,JERK。

Determination of Sight Distance on a Combined Crest and Circular Curve in a Three Dimensional Space

The sight distance(SD)on a two-dimensional(2-d)curve,namely,a vertical curve or a horizontal curve,has been well understood and documented for roadway geometric design in literature.In reality,three-dimensional(3-d)curves can be found along ramps,connectors,and often mountain roads.The sight distance on these 3-d curves,which may vary with driver’s location,has not been tackled in literature on an exact analytic setting.By integrating human-vehicle-roadway interaction,the formulas for computing the SD on a 3-d curve are derived the first time on an analytic framework.The crest curve SD that has been used in various literatures,can be deduced from these derived formulas as special limiting cases.Practitioners can easily apply theses userfriendly formulas or equations on a Microsoft Excel spread sheet to calculate 3-d SD on a roadway with sufficient roadside clearance.In addition,this framework can be extended easily to cope with various scenarios in which obstacles partially blocking driver’s sight are present in a roadway environment.

Determination of Onramp Weaving Length for Resolving Merging Dilemma

It is physically known that onramp merging may turn out to be difficult if the onramp(weaving/merging)length is too short because a driver under certain driving circumstances may find that either merging ahead or merging behind a neighboring vehicle on the adjacent highway lane cannot be completed.Various existing guidelines or design manuals provide no clear physical understanding and explanations to the design onramp weaving length but often based on evolved empirical experiences.By integrating human factors,vehicle dynamic characteristics,roadway surface condition,and the onramp weaving design into a single unified analytic framework,the onramp length required for a driver to merge into the highway traffic successfully is determined exactly with formulas and physical solutions to avoid the merging dilemma and enhance driving safety at highway interchanges.The design onramp weaving length is examined and evaluated with various foreseeable merging scenarios and physical examples.This analytic framework sheds light on the understanding of the onramp weaving the first time strictly on a physical human-vehicle-roadway interaction setting.Practitioners can easily apply these user friendly formulae and equations derived from the unified framework to calculate the onramp weaving length to resolve the merging dilemma and enhance driving safety for any highway interchanges.

Exact Sight Distance Determination on Compound Vertical and Horizontal Curves in the Presence of Road Barriers

The sight distance(SD)on a three-dimensional(3-d)compound curve has been studied recently in the absence of obstacles at road sides.Often,physical barriers are installed at road sides or in a roadway median for reducing potential collision severities;these rigid,semi-rigid,or even temporary cushion-type barriers can limit or reduce the driver’s sight distance,depending on their horizontal offset distances away from the nearest edge of traveled way(ETW).The closer a barrier to the ETW is,the shorter the driver’s sight distance would be.Since most barriers are constructed to prevent running-off road or crossing-median collisions,it is crucial to check whether the installation would reduce the driver’s sight distance and potentially cause other traffic collisions such as rear-end or side swipe collisions.In this paper,an exact analytic framework is formulated with derived equations the first time to calculate the sight distance on a 3-d compound curve in the presence of a median barrier,a roadside barrier,or a temporary cushion or barrier used for construction or other maintenance purposes.This framework provides an engineer a handy tool to examine the possible change of SD in the presence of a barrier and choose the required horizontal offset/clearance of a barrier from the nearest traveled way edge to meet certain design criteria or standards.This critical offset distance determined using this framework not only reinforces the importance of having roadside clearance recovery zones on highways but also provides a method to determine its horizontal clearance from a different standpoint.This analytic framework can easily be programmed into an Excel spreadsheet to evaluate the design of a physical barrier and its potential influence on sight distance along a 3-d compound horizontal and vertical curve.Transportation engineers or practitioners may find this design tool handy and useful once the programmed spreadsheet is saved in a shared or a flash/thumb drive.Note that the sight distance on a two-dimensional curve,such as a horizontal or a vertical curve,can be calculated straightforward as special cases using the programmed spreadsheet.

Integrating Visibility,Parking Restriction,and Driver’s Field View for Enhancing Pedestrian Crossing Safety

Pedestrians at a marked but unsignalized pedestrian crossing(Ped-Xing)must be made visible to drivers in the approaching traffic at a sufficient distance away from the crossing,and this distance is needed for stopping a vehicle before the leading Ped-Xing edge to avoid a potential traffic collision.In this paper,an exact analytic framework is established to integrate driver’s field view,driver’s perception-reaction,lighting condition,and parking restriction at a Ped-Xing for enhancing traffic operational safety.The size of the no parking zone by the Ped-Xing is determined exactly using equations derived from this framework.Additionally,this study sheds the light on mid-block Ped-Xing installation,which should be discouraged if parking is permitted alongside a street.Furthermore,additional visibility improvement measures at the unsignalized Ped-Xings may be needed for enhancing safe traffic operations at the crossings.

Deriving Sight Distance on a Compound Sag and Circular Curve in a Three Dimensional Space

Insufficient roadway sight distance(SD)may become a contribution factor to traffic collisions or other unsafe traffic maneuvers.The sight distance(SD)for a two-dimensional(2-d)sag or circular curve has been addressed in detail in various traffic engineering literatures.Although three-dimensional(3-d)compound sag and circular curves are often found along ramps,connectors,and mountain roads,the sight distances for these compound curves are yet to be analyzed on an exact analytic setting.By considering human-vehicle-roadway interaction,the formulas for computing the SD on a 3-d curve are derived the first time on a unified analytic framework.The 2-d sag curve SD can also be deduced from these derived formulas as special limiting cases.Practitioners can easily program these formulas or equations on a user-friendly Microsoft Excel spread sheet to calculate 3-d SD on most roadways with roadside clearance.This framework can be extended to estimate SD on roadways with obstacles partially blocking vehicle headlight beams.

A Multiscale Framework for Modeling Concrete Strength

Cementitious concrete is a composite mixture of coarse and fine aggregates,and other additives cemented into a C-S-H matrix.Practically,its strength may be determined by performing compression and tensile tests to specimens with certain sizes and shapes.In order to understand and enhance its strength,it becomes natural to seek the quantitative connections between fractured concrete surfaces and the strength of concrete across the scales of coarse,fine aggregates,and the CSH matrix with nano-scale structures.A multiscale theory across from the size of a test specimen down to the nano-scale of the known C-S-H matrix is proposed here to explain the concrete strength in terms of several physical scales associated with the concrete constituents based on energy conservation principle and fractal characterization of fractured concrete surfaces.When examined against experimental observations and test results,the proposed theory yields satisfactory estimation on nano-level molecular bonding,showing its effectiveness and importance for advancing our understanding of concrete strength.Additionally,the size effect of the testing concrete strength is derived from the proposed theory without making extra physical assumptions.

Ramp Metering Influence on Freeway Operational Safety near On-ramp Exits

Ramp metering has been widely installed in urban areas where congestion on a freeway or an expressway may occur recurrently during weekday peak periods to enhance mainline throughput and reduce system-wide delay.These operational benefits may also help reduce vehicular emissions and improve air quality in urban areas.However,the impact on traffic safety due to ramp metering hasn’t been explored in details before.Supported by physical understanding and arguments,we characterize the ramp metering influence on freeway safety by examining vehicular collisions near on-ramp exits within the ramp meter operating hours before and after the activation of the ramp metering.Collisions for a sample of 19 operating ramp meters along several freeways in northern California were collected and organized to show that ramp metering can help reduce freeway collisions at the vicinity of on-ramp exits.It was found that the average reductions on freeway collisions in the vicinity of an on-ramp exit are around 36%.Although most of the reduced collisions belong to the property damage only category,a 36%reduction shows the significant safety benefit of ramp metering.The traffic congestion induced by each collision,especially during peak hours when ramp metering is in operation,could last for an hour or two.Consequently,ramp metering must be contributing to the reduction of non-recurrent congestion in addition to mitigating recurrent congestion,which is better documented.This study strongly supports the implementation of ramp metering in California.

The Weaving Length Limit for Short Free Onramps

Onramp merging may be difficult if the onramp weaving/merging length is too short because a driver may find that even merging behind a neighboring large truck on the adjacent outside lane may not be completed safely.Because of insufficient weaving length for onramp acceleration,a slow merged vehicle may be rear-ended by a following vehicle on the outside lane when speed differential between the onramp vehicle and the following vehicle is relatively high.Nevertheless,short onramps at occasions are designed and built when right of way is constrained possibly by a variety of issues.The design onramp weaving length hasn’t been well explained physically in various existing guidelines or design manuals.Recently,a design paradigm,where human factors,vehicle dynamics,tire-road friction,and the onramp merging scenarios are integrated into a single framework,has been developed to resolve this merging difficulty.In this paper,the lower limit recommended for onramp weaving length needed for a driver to merge into the freeway traffic successfully is determined based on the physical solutions derived from the paradigm and a physical constraint for avoiding potential rear-end collisions between the slow merged vehicle and the following vehicle on freeway.This weaving length limit sets the minimal weaving length for safer free onramp merging and guides the practitioners/designers who encounter design situations where freeway right of way at onramp is limited.

Estimate Freeway Exit Sign Locations

Considering that a driver decides to exit a highway upon seeing the guide sign upstream of an exit,subsequently the driver in an inside lane or the middle lanes must move onto the outside lane prior to exiting.The concern is whether the driver can accomplish this task safely and smoothly.It is apparent that an upstream exit sign cannot be placed too close to an exit or too far beyond several exits upstream.The MUTCD recommends that the sign should be placed 1 mile and 2 miles upstream of an exit without explaining the reasons for selecting the 1 mile distance.By integrating driver decisions,vehicle acceleration characteristics,tire-road traction into a single analytic framework,the location upstream of an exit where an exit sign should be installed is determined for a driver to get off at the right exit successfully.Practitioners can easily apply these user friendly formulae and equations derived from the framework to compute the required distance‘D’between a highway exit and an upstream exit sign for guiding drivers to exit the highway safely.Additionally,parameters for these formulae can be adjusted to resemble various exiting scenarios.