Overview

Printable Overview, Introduction, and Getting Started

Krome Avenue is a 33-mile north-south route that bypasses Miami, Florida on the west side. It is essentially a rural route that has very little roadside development. Florida’s Turnpike is about 5 miles to the east, providing several east-west connections to Krome Avenue. Its two-lane configuration has limited capacity compared to other facilities such as freeways and multilane roadways. Most of the route now operates well within its capacity, except that some congestion has been observed at critical locations. This is a region of high population growth that is expected to generate continually increasing traffic volumes. Prompted primarily by safety considerations, the posted speeds have already been reduced below the 55 mph level typically found on open highways.  

In this case study, we will go through the process of identifying the goals, objectives and analysis tools for an investigation of the existing level of service on the entire route. We will then apply the analysis tools to assess the current performance of this route and to identify areas that are deficient. Finally, applying the same analysis tools, we will investigate some alternatives for correcting the deficiencies.  

The main purpose of the case study is to illustrate the concepts and practice of applying the analysis tools in general, and the Highway Capacity Manual (HCM) in particular. Much of the discussion will be based on a recently completed study of Krome Avenue that had similar goals and objectives. Several problems will be presented to illustrate the application of the tools and the interpretation of the results.  

Overview

Krome Avenue is a real highway and the data used in the problems represent actual field data. In some cases the alternative intersection improvements discussed in this case study were chosen for their illustrative value, and do not necessarily reflect the recommendations of the original study.

After studying this material, you should be able to:

Introduction

Printable Overview, Introduction, and Getting Started

Krome Avenue (SR 997) is one of the westernmost roadways in the Miami urban area, separating the developed portion of Miami from the Everglades, as shown in the map of Exhibit 3-1. There are no access controls that would give it any of the characteristics of a freeway. Traffic volumes are moderate; and congestion is not a major problem, except at a few critical intersections with important east-west arterials. A schematic overview of the entire route is presented in Exhibit 3-2.

This route has all of the characteristics of a two lane rural highway at the north end. It becomes increasingly urbanized (still retaining the two-lane configuration) and is clearly a signalized arterial at the south end of the study section. There are several intersections, both signalized and unsignalized, that require attention and analysis to determine what, if any, modifications should be made. Some of the intersections have unusual features that will be explored to create a better understanding of the application of the HCM.

Discussion:
Consider the situation described above and review the sketches and location map showing the street system. What steps would you need to go through to conduct a useful and relevant study of the Krome Avenue route identified in Exhibit 3-1? After you have listed these steps, continue to the next page to learn how we can apply the methods of the Highway Capacity Manual to address these issues and provide assistance to decision makers on how to improve this road facility.

Getting Started

Printable Overview, Introduction, and Getting Started

To begin this particular case study, we need first need to consider issues related to setting the scope, the goals and objectives, the analysis methodology, the sequencing of the analysis, the tools to use, and the data to employ. The following series of questions must be answered before the detailed work begins:

Getting Started

What are the goals, objectives, and scope?
We have learned from the Florida Department of Transportation (FDOT) staff that the goal of this project is to assess the current operation of Krome Avenue and to evaluate potential mitigation measures that could overcome the identified deficiencies. For the purposes of the HCMAG, we'll also use this case study to demonstrate the manner in which various procedures from the HCM should be selected and applied.

In order to meet the project goals set forth by FDOT staff, we'll need to address the following specific project objectives:

The scope of the study precludes major construction projects such as conversion of Krome Avenue from a two-lane facility to a multilane facility. Because of the simplicity inherent in rural settings, we will not go into great depth in the analysis of the intersection operations, except when a useful illustrative purpose exists. Other case studies in this Guide deal with more complex intersections in more urbanized settings.

Population growth in Florida is a complex issue that will be simplified for this study by assuming fixed annual growth rates for traffic volume projections.

Getting Started

What tools should we apply?
The study will focus on the procedures prescribed by the HCM for analysis of two-lane highways and signalized arterials. Arterial analysis also involves the HCM procedures that deal with signalized and unsignalized intersections. The relatively simple configuration of this essentially rural facility will allow us to perform all of the necessary tasks without seeking tools and models that are more complex than those offered by the HCM.

What analyses should be conducted?
There are many ways to classify traffic analysis problems that are appropriate for analysis with the HCM. Exhibit 3-3 below includes seven categories. The kinds of problems that are addressed in this chapter, within these seven categories, are highlighted in BLUE.

Getting Started

Who are the stakeholders and what are their issues?
The agencies and individuals who have an interest in this project include FDOT, the local communities through which Krome Avenue passes, the residents who abut or live near to the highway, and the commuters and others who use the facility on a regular basis. Although the facility users are a difficult group to speak to (they are hard to identify and they don't normally come to public hearings in their capacity as a road user), they are nevertheless represent a viewpoint that is equally as important as that of the other stakeholders.

The stakeholders are united around the goal of creating a safe and operationally efficient environment, but they have different ideas about how this might be accomplished. Some think the answer to current operational and safety problems is to modernize the roadway by adding new through lanes and exclusive turn lanes, while others think that such actions would raise speeds, increase volume, and create new problems at the interface points between the  urban and rural environments. Even with these preconceptions, all stakeholders recognize that it is too early in the process to be definitive about a preferred course of action, and they see this study as a necessary precursor to the development of alternative solutions, where facts are gathered and objective analyses are performed so that all future solution concepts can be judged against a common reference point.

Getting Started

What information is required to support the analyses?
Three types of input data are required, including geometric characteristics, operating parameters, and traffic data. Some of the data items will be used to determine the facility class designation, while other items are required to carry out the LOS estimation procedures. At this point, we are interested only in identifying what we need to know. The assumptions and application of default values will be indicated here, but the assignment of site-specific values and their use in the HCM procedures will be addressed in connection with each of the problems in this case study.

To establish the data requirements, it is necessary to refer to each of the facility chapters to identify the important determinants of the level of service on a facility. Referring to Chapter 10 (Urban Street Concepts), we are able to learn that the information in Exhibit 3-4 is needed to determine the arterial class:

Getting Started

Chapter 15 tells us that an arterial analysis is performed separately on each segment of the facility. The only piece of facility-wide data is the length of the analysis period, usually 15 minutes or one hour. A segment is usually terminated by a signalized intersection. The following information is needed for each segment to produce an estimate of the LOS for a signalized arterial:

Getting Started

We must refer to HCM Chapters 12 and 20 to determine the information required for LOS estimation on two-lane highways. Referring to Chapter 12 (Highway Concepts), we are able to learn that the determination of the highway Class is related more to the general nature of the highway and to motorist expectations than to quantitative field data. Unlike signalized arterials, there is no segmentation involved in a two-lane highway analysis. The facility is assumed to be homogeneous, and heterogeneous segments should be analyzed as separate facilities.

The following information is needed to produce an estimate of the LOS for a two-lane highway:

Getting Started

What growth rates should be expected for future traffic volumes?
Average Daily Traffic (ADT) counts along the corridor for the last six years (1996-2001) were obtained from the Florida Department of Transportation (FDOT). A regression analysis was performed on the six data points to find the best-fit linear and logarithmic traffic projections. While the average annual linear growth rate ranges from 5 to 21 percent, the logarithmic projection suggest an average annual 2.1 percent compounded growth to the year 2010 and a 1.5 percent compounded growth to 2020.

The logarithmic projection is more realistic of future growth for three reasons: 1) a linear rate of traffic growth is not physically possible to sustain for an indefinite period of time, 2) the historical ADT data from 2000 and 2001 in some cases already shows a trend that is starting to level off (that is, the rate of growth is decreasing), and 3) as roadways become more congested, the rate of traffic growth decreases. In addition, the future land-use plan for the corridor does not indicate a significant change over the existing land uses to warrant a continuation of the observed historical growth rates.

The applied growth rates recommended are as follows: 2.4 percent compounded annually for link volumes and intersection turning movement counts except for the through movement on Okeechobee Road, where a 2.7% annual growth rate is recommended.