An alternative classification of project delivery methods used in the United States building construction industry

Although many sources describe the project delivery methods available to owners, there is little empirical data on their defining characteristics. The objective of this research was to examine patterns in contract arrangements, procurement practices and compensation terms used in the US building construction industry. Survey data were collected for projects completed between 2008 and 2013 (N = 204) from owners and contractors belonging to large US professional organizations. A latent class analysis was used to identify five distinct patterns or ‘classes’ based upon eight characteristics of the project delivery process. These classes were defined as: (I) late builder and trade involvement, with an open, cost-based selection and lump sum contract (9% of projects in sample); (II) late builder and trade involvement, with a prequalified, cost-based selection and lump sum contract (19%); (III) early builder and late trade involvement, with a prequalified non-cost based selection and guaranteed maximum price (GMP) contract (26%); (IV) early builder and trade involvement, with a prequalified, cost-based selection and lump sum design-build (DB) contract (27%); (V) early builder and trade involvement, with a prequalified, non-cost based selection and GMP DB contract (18%). Compared to existing classifications of project delivery methods, these classes are data-driven typologies that represent how participants are procured and organized into a project team. The findings have implications as an alternative classification system in project delivery research and as guidance to owners considering their project delivery options.     

A descriptive analysis of light vehicle-heavy vehicle interactions using in situ driving data

Two recently completed on-road in situ (naturalistic) data collection efforts provided a large data set in which to conduct an examination of crashes, near-crashes, and crash-relevant conflicts (referred to as critical incidents throughout this paper) that occurred between light vehicles (LV) and heavy vehicles (HV). Video and non-video data collected during the two studies were used to characterize critical incidents that were recorded between LV and HV drivers. Across both studies, 210 LV-HV critical incidents were recorded. Of these, 78% were initiated by LV drivers, while the remaining 22% were initiated by HV drivers. Aggressive driving, on the part of the LV driver, was found to be the primary Contributing Factor for LV driver-initiated incidents. For HV driver-initiated incidents, the primary Contributing Factor was poor driving techniques. These results suggest that future efforts at addressing LV-HV interaction incidents should include focusing on aggressive LV drivers. Additionally, it is recommended that HV drivers might benefit from improved driver training that includes instruction on defensive driving skills. The in situ methodology provides an alternative to traditional crash databases, developed from police accident reports, for studying crash causation and driver behavior.     

Contributory factors to traffic crashes at signalized intersections in Hong Kong

Efficient geometric design and signal timing not only improve operational performance at signalized intersections by expanding capacity and reducing traffic delays, but also result in an appreciable reduction in traffic conflicts, and thus better road safety. Information on the incidence of crashes, traffic flow, geometric design, road environment, and traffic control at 262 signalized intersections in Hong Kong during 2002 and 2003 are incorporated into a crash prediction model. Poisson regression and negative binomial regression are used to quantify the influence of possible contributory factors on the incidence of killed and severe injury (KSI) crashes and slight injury crashes, respectively, while possible interventions by traffic flow are controlled. The results for the incidence of slight injury crashes reveal that the road environment, degree of curvature, and presence of tram stops are significant factors, and that traffic volume has a diminishing effect on the crash risk. The presence of tram stops, number of pedestrian streams, road environment, proportion of commercial vehicles, average lane width, and degree of curvature increase the risk of KSI crashes, but the effect of traffic volume is negligible.     

Do laboratory frontal crash test programs predict driver fatality risk? Evidence from within vehicle line variation in test ratings

A number of studies have examined whether the National Highway Traffic Safety Administration's (NHTSA) frontal crash test results reliably indicate the risk of fatality or injury in serious crashes. The conclusions of these studies are mixed. Generally, studies that examine crashes in the circumstances as close as possible to those of the laboratory test find that crash test results do predict real-world risk, but studies of crashes outside those specific circumstances find either no support for the predictive validity of crash test results or limited support with important inconsistencies. We provide a new test of the predictive validity of the crash test results using information from multiple crash tests within vehicle lines, thus controlling for systematic differences in driver behavior across vehicle lines. Among drivers of passenger cars, we find large, statistically significant differences in fatality risk for vehicles with one- to four-star NHTSA ratings versus a five-star rating. We also examine the Insurance Institute for Highway Safety's frontal offset crash test, though our sample of vehicle lines tested twice or more is considerably smaller than for NHTSA ratings. Our results also support the predictive validity of the frontal offset crash test results for passenger cars, but not for trucks.     

Misunderstanding of right-of-way rules at various pedestrian crossing types: observational study and survey

Misunderstanding of right-of-way rules may contribute to pedestrian trauma, especially at crossings where pedestrian and traffic signals appear to give contradictory messages. Two thousand eight hundred and fifty-four pedestrians were observed crossing at signal-controlled intersections to compare attention to traffic for different combinations of pedestrian and traffic signals. In addition, a survey was conducted at signal-controlled intersections and nearby car parks in metropolitan and rural areas. Five hundred and seventy-four participants took the role of pedestrian or driver when responding to questions regarding beliefs about pedestrian right-of-way for a range of situations at signal-controlled crossings, zebra crossings, and unmarked sections of road (specifically: alone, with pedestrian refuge, or paved). Results suggest that at signal-controlled crossings pedestrian right-of-way is erroneously thought to be influenced by the pedestrian signal. Many respondents thought that a pedestrian refuge or paving gave a pedestrian right-of-way at an otherwise unmarked section of road. In many situations more than 20% of both drivers and pedestrians reported that they would take right-of-way. Pedestrian crossing types should be rationalised, and education should be provided regarding rules and responsibilities at available crossings.     

Traffic signal phasing at intersections to improve safety for alcohol-affected pedestrians

Alcohol-affected pedestrians are among the highest-risk groups involved in pedestrian casualty crashes. This paper investigates the opportunities to use a modified form of traffic signal operation during high-risk periods and at high-risk locations to reduce alcohol-affected pedestrian crashes and the severity of injuries that might otherwise occur. The 'Dwell-on-Red' treatment involves displaying a red traffic signal to all vehicle directions during periods when no vehicular traffic is detected, so that drivers approach high-risk intersections at a lower speed than if a green signal were displayed. Vehicle speed data were collected before and after treatment activation at both a control and treatment site. Speed data were collected both 30 m prior to and at the intersection stop line. The treatment was associated with a reduction in mean vehicle speeds of 3.9 kph (9%) and 11.0 kph (28%) at 30 m and stop line collection points, respectively, and substantial reductions in the proportion of vehicles travelling at threatening speeds with regard to the severity of pedestrian injury. Other important road safety concerns may also benefit from this form of traffic signal modification, and it is recommended that other areas of application be explored, including the other severe trauma categories typically concentrated around signalised intersections.     

Hazard perception and driving experience among novice drivers

The crash risk of novice drivers decreases rapidly during the first few months of post-licensing driving, indicating that some important safety-relevant traffic skills are learnt during this period. The present study tested the hypothesis that the risk decrease is related to improved hazard perception skills. A video-based hazard perception/reaction test, measuring reaction times to 31 traffic scenes, was administered to three groups of drivers, having held a licence for 1, 5, and 9 months, respectively, and to a group of drivers who had held their licences for several years. Average reaction times tended to decrease with experience, but the decrease was not significant. There were some significant differences in the expected direction for individual test items, indicating a possible effect of experience. One half of the situations were presented together with a secondary task, in order to investigate effects of increased mental load on hazard perception. Male novice drivers had relatively longer reaction times with the secondary task, compared to both female novice drivers and male experienced drivers. It is concluded that hazard perception as tested here is probably only a minor factor in explaining the initial risk decrease among novice drivers.     

Quantifying effects of ramp metering on freeway safety

This study presents a real-time crash prediction model and uses this model to investigate the effect of the local traffic-responsive ramp metering strategy on freeway safety. Safety benefits of ramp metering are quantified in terms of the reduced crash potential estimated by the real-time crash prediction model. Driver responses to ramp metering and the consequent traffic flow changes were observed using a microscopic traffic simulation model and crash potential was estimated for a 14.8 km section of I-880 in Hayward, California and a hypothetical isolated on-ramp network. The results showed that ramp metering reduced crash potential by 5-37% compared to the no-control case. It was found that safety benefits of local ramp metering strategy were only restricted to the freeway sections in the vicinity of the ramp, and were highly dependent on the existing traffic conditions and the spatial extent over which the evaluation was conducted. The results provide some insight into how a local ramp metering strategy can be modified to improve safety (by reducing total crash potential) on longer stretch of freeways over a wide range of traffic conditions.     

Are car drivers holding a motorcycle licence less responsible for motorcycle--car crash occurrence? A non-parametric approach

The purpose of this work is to evaluate the effect of a specific motorcycle licence, held by car drivers, in responsibility for motorcycle-car crashes. The data were provided by a multicentric case-control study (MAIDS) regarding the risk of crash and serious injuries of motorcyclists. A non-parametric method, classification and regression tree (CART), was used to accomplish the objective, and then compared to standard unconditional logistic regression. Drivers owning a motorcycle licence turned out to be less responsible for motorcycle-car crashes than drivers who do not have one; both types of analysis are consistent with this result. It is reasonable to assume that car drivers who hold a motorcycle licence have acquired more ability in riding and controlling two wheeled vehicles than drivers without a licence, and this may help them in predicting motorcycles manoeuvres.