This report presents the results of a review of long held contentions regarding driver choice of speed and reaction to speed limits. Areas of concern that were studied included influence of the roadway environment, reaction to school speed zones and reaction to warning flashers. Results of the review show that drivers do vary their speed under differing conditions, they do not react as desired to lowered speed limits or to passive signing. They do lower speeds when they see a warning flasher in conjunction with limit signs, but not as much as is requested. There was evidence too that in some zones a lower limit may result In a more hazardous situation.
Sand-filled barrel crash cushions and the Minnesota bullnose guardrail are two types of impact attenuators which protect errant vehicles from collisions with roadside hazards. This study is the result of a need to evaluate the effectiveness of these two devices in reducing the severity of accidents.
The emphasis of this study was placed on the safety performance of crash cushions using the National Cooperative Highway Research Program (NCHRP) Report 230 crash testing criteria as guidelines for evaluation. Results of full-scale crash testing of these two devices were used as a model of actual accidents involving these impact attenuators.
In 1965 the Minnesota Legislature amended the State Statutes to permit drivers to make a right turn on a red light (RTOR) after stopping, but only where "permissive" signing (Figure I) had been posted. When study and experience failed to reveal evidence which would oppose the use of RTOR, the law was renewed in 1967 and again in 1969. Continued favorable experience led to a change from the "permissive sign" RTOR to a "basic law" RTOR, which became effective on July 1, 1972. On that date, the RTOR became legal except where banned by appropriate signing (Figure II).
During the seven years of permissive sign RTOR, most jurisdictions in the State took advantage of the law (although to varying extents). Initially, signs were placed conservatively and no major problems developed. Gradually, the use expanded until the signs became quite common. Since July 1, 1972 the statewide practice has been to ban the movement only where geometries are unfavorable, where sight distance is limited, or where unusual pedestrian situations exist. The City of Minneapolis is the only jurisdiction with a substantial number of signs posted.
Since no warrants for RTOR had been formally accepted and discussion on the movement continued, a study was conducted to compare driver performance and delay under the pre July 1 permissive signing and the post July 1 basic law. Subsequently, 54 intersections were selected for delay and compliance studies.
In April 1980, the Minnesota Department of Transportation (Mn/DOT) issued a written policy requiring, in most cases, the use of red, yellow and green left turn arrow indications rather than programmed circular (ball) indications for left turn signals. Contracts let since 1981 have specified 12" red, yellow and green arrows for exclusive left turn phasing.
In spite of the apparent success of arrow indications, there remains some non-uniformity of use and debate over the merits of the red arrow and the red ball. This present study, therefore, addresses the use, safety and acceptance of red arrow indications.
Recently the Minnesota Department of Transportation surveyed state traffic officials in order to assess their use of, and experience with traffic signal change interval advance warning devices. A total of 44 responses from 39 states were returned. Results are shown in Tables 1 and 2.
Of the states returning the completed survey forms, 20 reported using some form of advance warning device. These signs were activated either prior to yellow phase or at start of yellow. The most common sign legend used was "Prepare to stop when flashing", or slight variations of this (e.g. "Be prepared to stop when flashing"). Also fairly common among those states utilizing advance warning devices were blank out messages and W3- 3 "Signal Ahead" signs with flashers activated for signal change intervals. Table 1 presents this information for the 20 states using these devices.
This report presents an evaluation of the use of citizen's band (C.B.) radio in the I-35W traffic management system. The I-35W system, which extends along a 17 mile section of freeway south of downtown Minneapolis, has been in operation since April, 1974. This system includes ramp control signals, bypass ramps for high occupancy vehicles, a closed circuit television (CCTV) network, a motorist information program, and an incident detection and response program. Operation of the system is computer coordinated from the Traffic Management Center (TMC) near downtown Minneapolis. A listing of reports which document the design details, system hardware and software, and system evaluation is presented in the Appendix.
This report presents an evaluation of the first five years of operation for the I-35W traffic management system, which extends along a 17 mile section of freeway south of downtown Minneapolis. The system was developed as part of the I-35W Urban Corridor Demonstration Project which combined the benefits of traffic management with express bus transit service.
Roadway geometries, vehicle type and traffic flow characteristics are factors commonly referred to in discussions of freeway capacity, primarily because they are significant and can be influenced by the application of traffic engineering techniques. There is another factor, or rather group of related factors, that can be classified under the broad term "weather," which have often been ignored in the sense of quantitative studies, although traffic engineers and motorists alike have cursed and praised many a day's weather. One reason weather factors have been largely neglected is chat they are, unlike geometries, not directly in the control of engineers. They also are discontinuous and therefore difficult to plan on or respond to - after all, if there was always two inches of snow on the pavement, or if it continually rained, we could make adjustments. As it is, one common reaction to bad weather is simple despair.
Recently, attention has been paid to flexible traffic management techniques which, although still not putting engineers in control of the weather, allow management personnel to at least positively respond to weather conditions. An example of such flexible traffic management is the use of a metered freeway system, such as that along I-35W south of Minneapolis in Minnesota. Although it cannot hold off a snowstorm, such a system allows the input to the freeway to be controlled so that the reduced capacity is not exceeded and the accidents connected with bad weather are avoided. The question which management personnel must answer to respond appropriately to a particular weather situation is, "given this much rain (or snow or wind) how much will traffic flow be affected; that is, how severe should my response be?" Unless system operators know to what extent a particular situation threatens to reduce traffic flow, they can not respond confidently and appropriately. Because flexible traffic management is becoming increasingly common as a way to maximize the use of highway facilities when energy costs are high and construction dollars dwindling, it is time to take a quantitative look at the impact of weather on freeway capacity.
