Chapter VIII

PUBLIC SAFETY

STANDING COMMITTEE-1925

ALCIDE CHAUSSÉ, Chairman..

H. G. PERRING..

W. C. E. BECKER.

P. C. PAINTER.

.Montreal, Canada

. Baltimore, Md. ..St. Louis, Mo. .Greensboro, N. C.

COMMITTEE MADE NO REPORT

THE THREE-LANE TWO-WAY ROADWAY

By Arthur H. Blanchard, Professor of Highway Engineering and Highway Transport, University of Michigan

A three-lane two-way roadway is one upon which the traffic movements are in both directions and which is only wide enough for three moving vehicles to be abreast.

The data and conclusions relative to the status of the threelane two-way roadway are based primarily on a joint investigation by the Michigan State Highway Department and the Division of Highway Engineering and Highway Transport of the University of Michigan. Most of the field investigations were made by Professor B. T. Schad of the University of Dayton and Professor Frank H. Derby of Washington University, St. Louis.

The three-lane two-way roadway has been generally employed where it was considered that the highway would be subjected to an amount of traffic exceeding the traffic capacity of a twolane roadway and, in some cases, under conditions where it was not considered economical or practicable to construct a fourlane roadway.

As the ideal movement of traffic might be said to be such as to permit each vehicle to continuously travel at the speed desired, but within the legal regulation limit, it is apparent that the traffic capacity of a two-lane roadway from this standpoint would be very low. Traffic capacity, considered from the view

point of the maximum number of vehicles which can pass a given point in a given period, far exceeds the capacity which has been termed ideal. For two-lane roadways the actual capacity varies within wide limits, as it depends on many variables, including the width of roadway, the location of the lanes in which vehicles travel, the widths of the various vehicles, the speeds and distances apart at which vehicles travel, the number of vehicles traveling at each speed, the kind and number of vehicles traveling in groups, and the relative amount and character of traffic in each direction.

It is evident that the use of a three-lane roadway generally will permit vehicles to pass each other with greater frequency than the vehicles of the same traffic would be able to pass on a two-lane roadway.

Investigations indicate that the twenty-foot roadway is sufficiently wide to provide adequate clearances between the sides. of vehicles and the edges of the roadway and between passing vehicles. On one roadway under investigation, where the maximum hourly traffic was 750 vehicles, the clearance between vehicles was three to four feet. No instances of three vehicles being abreast were noted. As the average width of three automobiles is sixteen feet six inches, it is evident that there would not be satisfactory clearances between the vehicles and between. the vehicles and the edges of the roadway.

On twenty-four foot roadways the United States Bureau of Public Roads found that the average clearance between automobiles was 6.1 feet, and between trucks 5.1 feet. In an investigation in Michigan of a roadway of this width having a maximum hourly traffic of 1250 vehicles, the clearance between automobiles was found to vary from five feet to six feet six inches and between trucks from four feet to six feet. At the point of observation it was noted that three vehicles were abreast from one to seven times per hour, in each case all the vehicles being automobiles. Considering that the average width of an automobile is five feet six inches, the natural conclusion agrees with observed observations-namely, that the vehicle occupying the middle lane forced its passage between the other two vehicles. Generally fast and reckless drivers constituted the majority of operators who endeavored to use the middle lane.

The results of the investigations indicate that twenty-two and twenty-four-foot roadways are not required for two lanes of

traffic and that they are not wide enough to serve generally as three-lane roadways.

Roadways between twenty-four and thirty feet in width usually have middle lanes of sufficient widths to encourage their utilization. On a thirty-foot roadway, having a maximum hourly traffic of 1050 vehicles, it was found that the clearance between automobiles varied from eight to ten feet and between motor trucks from five to nine feet. At the point of observation three vehicles were abreast seven to twenty-one times per hour. It is evident that the middle lane of a thirty-foot roadway is very generally utilized.

The illustrative data submitted indicates that roadways of from twenty-four to thirty feet in width are used as three-lane two-way roadways. Unfortunately, however, traffic movements on the middle lane cannot be governed by a right-of-way regulation. Hence the use of three-lane two-way roadways provides conditions under which accidents may frequently occur. Therefore, from the standpoint of encouraging design which will promote the safe utilization of highways, the conclusion is expressed that the four-lane two-way roadway should be used when the highway transport survey indicates that the traffic capacity of a two-lane two-way roadway will be exceeded.

DISCUSSION

SECRETARY BROWN: Mr. President, I would like to say just a word. I agree thoroughly with Mr. Blanchard's conclusions, not from the study of the three-lane roadway, but from the study of a two-lane roadway. I have frequently traveled on a two-lane roadway which is 18 feet wide and so it does not have the clearance which he has with the 20-foot roadway. The difficulty, as he says, is in trying to pass the line of vehicles ahead. The frequency of the passage of vehicles is anywhere from one a minute to, say, fifteen a minute (40 to 47 a minute occasionally on a special day). When you get 15 a minute it means they are often very close together, and you have no opportunity whatever to get out of one lane and pass the vehicle, or the line of vehicles that is ahead of you, especially when you are not permitted to cut into that line. In the case of the twolane roadway you have to wait until the 15 vehicles are passed before you can make your trial, and if you are a slow driver you will have to wait longer than that, because, especially at

night, it is quite difficult to judge speeds sufficiently well to be able to pass without danger. That means, of course, that you are held up, and the other line of vehicles on the other lane is held up by the slow driver in front, who is driving, perhaps 15 miles an hour-driving with one hand, or something of that sort. The people who are behind him are trying to get ahead, and they do not see a chance to get by on account of the vehicles on the other side, and finally you get a dozen or fifteen of them lined up behind each other just far enough apart so that they are not in danger of running into each other, and that is pretty close, because the fellow ahead is only runinng 15 or perhaps 20 miles an hour. It is the reckless driver who tries to pass when some one from the other lane is trying the same thing. The minimum speed, therefore, is of quite as much importance as the maximum speed. I had this experience: Our maximum speed was 30 miles an hour, and it would seem to be fairly easy to get by those ahead on 30 miles, if we had a slow driver in front; but our maximum now is 45 miles an hour, and it seems to me it has become very much more dangerous, because the men who travel 45 miles an hour are more frequent than they used to be. Of course, we have had them all the time, but they were skipping the traffic cop if they ran over 30 until this year. The reckless driver tries more frequently now, and I think the traffic on the road when crowded has been slowed up very materially by the increase in the maximum rate of travel which is allowed. I can see very readily that if we had a three-lane roadway we would have accidents every few minutes; but as it stands at present we do not have them so very often. Occasionally you see somebody who has been hit by somebody who tried to crowd him off the road, because he was trying to get by and was hog enough to try to push the other fellow out. I know my wife was driving one day with a lot of girls in the car, and she was chased off onto the sand on the side of the road and nearly tipped over by some fellow who was trying to pass in this same way and crowded her off. She was easy to crowd, of course. So there is a real difficulty with the faster travel on a two-lane roadway. If we had the three-lane roadway it would be lined with wrecks all the time.

PRESIDENT DALTON: Is there any further discussion?

GEO. W. CRAIG: Mr. Chairman, I feel that this discussion is