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Lessons Every Transportation Engineer and Planner Need to Learn

Posted on: Sunday, 4 May 2008, 03:00 CDT

By Stein, Howard S

THE FIELD OF TRAFFIC ENGINEERING/PLANNING IS UNIQUE WHEN COMPARED TO OTHER DISCIPLINES DUE TO THE INVOLVEMENT OF THE PUBLIC AND THEIR PERCEPTIONS. THIS FEATURE HIGHLIGHTS KEY LESSONS LEARNED FROM MANY YEARS OF WORKING FOR A WIDE RANGE OF CLIENTS AND COMMUNITIES. THESE LESSONS ARE INTENDED TO HELP YOUNG PROFESSIONALS AVOID MANY OF THE PITFALLS THE AUTHOR ENCOUNTERED DURING HIS CAREER. THIS FEATURE PRESENTS FIVE KEY lessons learned from more than 25 years of experience as a traffic engineer and planner. These lessons are intended to help young professionals avoid many of the pitfalls the author encountered during his career.

The field of traffic engineering/planning is unique when compared to other engineering disciplines due to the involvement of the public and their perceptions. Most people drive vehicles and form their own opinions about the roadway system. Typically, the public significantly overestimates its travel times and delays at congested intersections.

In addition, most transportation projects contain some form of public comment or participation via hearings, workshops, surveys and other forums. Other engineers, such as electrical, mechanical and chemical engineers, do not have this direct public scrutiny. As a result, traffic engineers/planners not only have to develop technical expertise, they also have to be able to present and explain their work in public forums.

IESSON 1: ONlY TRAFFIC ENGINEERS/ PIANNERS UNDERSTAND THE CONCEPT OF LEVEL OF SERVICE

The traffic engineering profession has spent a great deal of effort to develop and define the concept of level of service (LOS). These methods and criteria have a long history of conceptualizing and analyzing many operational characteristics of transportation facilities, especially intersections. These models also have been validated in the field. They allow engineers, planners and jurisdiction staff to objectively evaluate the impact of a new development or to assess the benefits of potential roadway or intersection improvements.

The problem is that the average motorist does not understand the concept of LOS. Most people tend to think in terms of total travel time to their destination. Furthermore, motorists often significantly overestimate how long these trips take, especially how long they wait at a particular congested intersection.

At the same time, motorists do not recognize how well the roadway system operates along a corridor, but they do note long delays at one major intersection. To address this perception, many jurisdictions recently have adopted both intersection LOS and travel time/vehicle speed criteria for corridors.

Regarding intersection delays, motorists often say that they have to wait 2 minutes or longer to turn left from a minor street. Videotaping traffic operations along minor street approaches where significant congestion is expected often is useful because it allows evaluation of actual vehicle delays.

Due to several factors, these measured delays can be significantly lower than the results from standard Highway Capacity Manual (HCM) software estimates. The most common reason for this difference is the impact of a nearby signalized intersection that creates distinct platoons of vehicles rather than the random flow pattern assumed by HCM methods.

Another factor is the availability of twostage left-turn maneuvers from the minor street. The HCM procedures contain methods for adjusting for these situations. To confirm the impact of these factors, it is recommended to observe the approach in question several times to validate its actual traffic operations and vehicle delays.

In addition, there are other special situations where standard LOS procedures will underestimate traffic congestion. One example is at an unsignalized intersection with heavy right-turn volumes on the minor street and a single-lane approach. Figure Ia presents baseline traffic flows at a typical low-volume intersection. The minor approach is LOS B, with an average control vehicle delay of 10.3 seconds per vehicle and a volume-to-capacity (V/C) ratio of 0.08.

Figure 1b presents the same intersection where the volumes on the minor street have been doubled. For this later scenario, most people would expect that delays on the minor approach also would double or at least would increase significandy. HCM procedures estimate that this minor approach will have LOS B with a V/C ratio of 0.16 (double the baseline case) but an average control delay of 10.8 seconds per vehicle, which is an increase of only 0.5 second.

These delay results appear counterintuitive. The answer is that by adding a large number of right turns with less delay per vehicle compared to a few left turns with longer delay, the combined average delay on the approach may not change significandy. To address this, engineers/planners may consider reporting higher delays riian the standard HCM results within the same LOS range and more consistent with the V/C ratio. By doing this, the integrity of the results is maintained and a detailed presentation of this paradox at a public hearing or workshop is avoided.

Another example where standard HCM procedures do not accurately estimate vehicle delays or V/C ratios occurs in resort/ tourist communities along the main street during peak summer days. Typical analysis of intersection or arterial capacity often will estimate LOS B or C. However, any resident will tell you that traffic crawls along the main street all summer. The problem is that many motorists slow or even stop in the middle of the street to look at adjacent businesses and/or search for parking spaces. This scenario is typical, and credibility with the community will be lost if the standard results from HCM/Highway Capacity Software procedures are presented.

The solution to this scenario is to adjust the saturation flow parameters to reflect the lower capacity of the corridor. Unfortunately, there is no specific guidance to offer about what value to use for this scenario. Traffic engineers/planners should use professional judgment regarding how low to set this parameter. Calibrating the analysis by videotaping traffic operations at a couple of critical intersections is possible.

LESSON 2: TRAFFIC ENGINEERS/ PLANNERS KNOW TOO MUCH MATH

This lesson is similar to lesson 1 but also applies to other types of analyses that engineers and planners perform. Traffic impact and planning studies often contain many numbers and analyses that are totally incomprehensible and/or misinterpreted by the average person. Two situations in which this commonly occurs are in calculating the trip generation of a development and in estimating future traffic volumes.

Most traffic impact studies are based on peak-hour volumes, but the public tends to focus on average daily traffic (ADT) volumes, which, of course, are larger numbers. The solution to this is to carefully explain trip generation calculations to the public and the role of ADT and peak-hour volumes in the analysis performed. It also is important to make sure the proportion of trips that may come from pass-by or diverted traffic is documented, if applicable. Most people appear to understand these concepts.

Although ITEs Trip Generation does not include pass-by factors for ADT, engineering judgment should be used to determine how to factor p.m. peak-hour pass-by data in the Trip Generation Handbook to apply to ADT as well as a.m. peakhour trip generation estimates.

Many long-range corridor studies tend to give the impression that traffic volume estimates five to 20 years into the future are precise to the nearest vehicle. In some studies, these future volumes are calculated by conducting existing traffic counts and then applying a general growth factor to all volumes in the study area.

Problems often arise regarding turns from minor streets and turn volumes from the main street or from the highway corridor onto minor streets. Typically, current counts for these turn movements are relatively low, (zero to five vehicles) (see Figure 2). Even if a high growth factor is applied, such as 30 percent, the future volume will be zero to seven vehicles (1.3 x 0-5 vehicles).

However, land adjacent to this corridor typically has significant development potential, and this traditional method grossly underestimates these turn volumes. This underestimating can have major consequences when turn-lane, signal warrant and cross-section analyses are conducted. The solution is to consider local growth trends as well as regional growth factors when estimating these future volumes.

The preferred method is to make specific assumptions about the build-out potential of the adjacent areas and to estimate their trip generation explicitly. These volumes then would be assigned to specific intersections throughout the roadway network. In some cases, however, this level of detail is too speculative.

As shown in Figure 2, at a minimum, one simply could assume reasonable values for these turn volumes, such as 25 vehicles per hour for turns from minor local streets and 50-100 vehicles making turns to/from major collector or minor arterial streets. The key is try to be realistic about estimating future traffic volumes and not blindly apply general growth factors. Another problem arises in how the results of long-term traffic volume projections are interpreted and applied. Even if the guidelines above are followed, it must always be kept in mind that these volumes are estimates. It is the nature of engineers and planners to be conservative; that is, to use growth factors and trip generation assumptions that would tend to overstate future volumes and congestion. At the same time, turn- lane, signal warrant and cross-section analyses are based on these volume estimates and may yield findings that are within 10 to 20 vehicles of meeting volume criteria for improvements.

In some cases, such as where a five-lane section is recommended over a three-lane section, the impacts of these choices on local residents and businesses along the corridor must be realized. Public and advisory committee members may overreact to these findings, sometimes opposing or delaying roadway projects because of the additional right of way required for the more robust improvement scenario.

The solution to these problems is to conduct sensitivity analyses, evaluating two to three scenarios including low-, mediumand high-growth assumptions, to evaluate what roadway improvements are needed. If the roadway improvements do not vary between these scenarios, this approach will help validate recommendations and build consensus among stakeholders.

In addition, the traffic engineer/planner may recommend that improvements be done in phases but ensure that any short-term improvements constructed (and future land developments that occur along the corridor) not preclude longterm improvements that may be needed.

LESSON 3: THE PUBLIC OFTEN ARE THE REAL LOCAL TRAFFIC EXPERTS

Although average citizens do not speak "traffic engineerese," it is helpful to listen to their concerns and ideas from at least a comprehensive point of view. A typical traffic study is based on one or two days of counts and observations. Even so, some professionals discount comments from the public, who travel these roadways on a daily basis, as local griping. These residents know the real congestion points and often have practical ideas to address them.

Moreover, it is important to understand their local travel patterns. In small communities with a state highway as the main roadway, conflicts often arise between moving traffic along the highway versus local trips, access to local businesses and key land uses, especially the post office and schools. These local experts know the short cuts and have good ideas about where new links would be useful.

Furthermore, many communities have significant mid-day or early afternoon peak hours that are comparable to the traditional 4:00- 6:00 p.m. peak hour. Travel patterns during these other periods typically are very different than commuter peak hours. The lesson is to carefully listen to public comments, even though they may exaggerate congestion or may not be technical, and hear the overall message and ideas presented.

LESSON 4: VISIT THE STUDY AREA SEVERAL TIMES DURING THE PROJECT, ESPECIALLY DURING THE MOST RELEVANT TIME PERIODS AND JUST BEFORE KEY MEETINGS

Many intersections and corridors have unique characteristics that are not captured by standard traffic counts. Traffic operations throughout the study area can be complicated by special circumstances such as sight distance limitations, queuing caused by short turn bays and/or poor access management. To observe these impacts, the traffic engineer/planner needs to visit the study area during critical peak hours.

In one recent case, congestion at an intersection was related to back-ups occurring at a left-turn bay. The initial site visit during the "critical" p.m. peak hour did not reveal any congestion issues. Further investigation found that the problem actually was in the morning due to traffic leaving a drive-through espresso stand that cut into through traffic (forcing these vehicles to stop) to get into the left-turn bay.

If safety problems are an issue, it is important to examine how and when these crashes occur. If they occur at night, the site should be visited at night. Many intersections look different at night compared to daytime hours. In a recent project, several rear- end crashes that resulted in serious injuries occurred at a skewed intersection (see Figure 3). It was perplexing that these crashes occurred on the main roadway and not the minor street approach. The local traffic engineer conducted a site visit during the p.m. peak hour and could not find any problems at this intersection.

The review of the crash reports found that all of these crashes occurred at night. A nighttime site visit found that the STOP sign on the minor approach was angled so that drivers on the major street also could see the sign. As a result, unfamiliar drivers could have interpreted this as their stop control. This major roadway was a tourist route, and a review of the crashes found that all the lead drivers in these rear-end crashes had non-local addresses.

The likely scenario was that tourist drivers saw the skewed STOP sign and stopped/slowed to determine if the stop control applied to them. Unfortunately, a local resident was following behind and did not expect a stopped/slowed vehicle ahead, and a rear-end collision occurred at relatively high speed.

Finally, it is always wise to visit the study area before a project hearing or major milestone meeting. Invariably, 6 months to a year may elapse between the date of the first site reconnaissance and this meeting date, and new developments and/or roadway improvements may have occurred in the interim. These changes could significantly impact many aspects of the analysis, design, or presentation.

LESSON 5: UNDERSTAND EACH JURISDICTION'S TRAFFIC STUDY REQUIREMENTS, DESIGN STANDARDS AND HEARING/ MEETING PROCEDURES

During 2005, the author's office prepared reports and plans for more than 20 different jurisdictions covering three states. Many of them had very specific requirements related to concurrency, traffic counts, estimating future volumes and other components of transportation planning studies. For example, traffic study impact areas in some jurisdictions were negotiated; others had specific volume criteria. The same was true of roadway design standards and drawing formats.

While many standards tend to be similar, most jurisdictions vary in their definitions of road cross-sections and many minor but significant characteristics. For larger projects, it is common to develop a set of analysis/design assumptions, including formal letter reports/memoranda that memorialize these decisions. A typical problem is when staff changes at the agency and decisions made early in the project are not well documented for the new staff.

A solution to these problems is to practice active listening techniques including sending team/jurisdiction staff members summary memos detailing the notes of key project meetings, assumptions, or other key milestone and decision points. It is further recommended to keep a project log of milestones, deliverables, e-mails, phone calls and other important aspects of the project. The log could be kept using commercial software or a system of simple Excel spreadsheet or Word documents. The most important consideration is to choose a system that staff will use.

With this project chronology, it is easy to quickly look up and document when and what occurred as a project progresses, especially items that result in revisions and change orders. It sometimes is difficult to keep these project logs current, but they are invaluable when it comes time to invoice clients for extra work performed or to revisit the background for a key project decision.

Finally, the methods and rules for conducting public meetings and hearings vary significandy among jurisdictions. Some are conducted by professional hearing examiners (often attorneys); others are conducted by volunteer or paid commissioners or design review boards. Presentations must consider the experience and knowledge of the audience.

There also are subtle differences in how these meetings are conducted. Some jurisdictions limit an applicant's presentation time to 20-30 minutes; others allow unlimited time as long as the presentation materials are relevant to the jurisdiction's approval criteria. There also can be rules about introducing new evidence at a hearing and what can be brought up as rebuttal or final summation.

Understanding these differences will significantly impact the type of presentation and materials that need to be prepared as well as how the formal record and approval of the project can be achieved.

CONCLUSION

The traffic engineering and planning profession is unlike other engineering fields because of the types of work performed and the relation to the public. The lessons and solutions discussed in this feature present points of view and approaches that should help novice (and perhaps even experienced) professionals understand and address many pitfalls the author experienced during his career.

ACKNOWLEDGEMENTS

I would like to gratefully acknowledge the help of the staff of CTS Engineers, particularly Arshad Syed, E.I.T., for their support in preparing this article and developing these practices and policies over the years.

BY HOWARD S. STEIN, P.E., PTOE

HOWARD S. STEIN, P.E., PTOE, is a senior transportation engineer for WilsonMiller in Tampa, FL, USA. This article was originally prepared while he served as vice president of CTS Engineers in Hilkboro, OR, USA. He is a member of ITE.

Copyright Institute of Transportation Engineers Apr 2008

(c) 2008 Institute of Transportation Engineers. ITE Journal. Provided by ProQuest Information and Learning. All rights Reserved.

Source: Institute of Transportation Engineers. ITE Journal

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