VII. Congestion Management
System
“Within a transportation
management area, the transportation planning process under this section shall
include a congestion management system that provides for effective management
of new and existing transportation facilities eligible for funding under this
title and chapter 53 of title 49 through the use of travel demand reduction and
operational management strategies.”
23 U.S.C. 134 (i)(3)
he CDTC adopted its Congestion Management
System (CMS) in December 1995, building upon its 1993 report entitled Critical
Congestion Corridors in the Capital District. Congestion mitigation is directly related to CDTC’s New Visions goals concerning mobility,
wherein mobility is best maintained by providing for convenient travel while
reducing inefficient travel behavior.
The CMS incorporates the full range of the New Visions core
performance measures; for congestion, the core performance measure is excess
delay. Person hours are used for all
values except for truck traffic, for which vehicle hours are considered more
relevant. The set of principles used in
the CMS is shown in Table XX.
Table
3: CDTC’s
CMS Principles |
|
1 |
Management
of demand is preferable to accommodation of single-occupant demand growth. |
2 |
Cost-effective
operational actions are preferable to physical highway capacity expansion |
3 |
Land use
management is critical to the protection of transportation system investment. |
4 |
Capital
projects designed to provide significant physical highway capacity expansion
are appropriate congestion management actions only under certain conditions. |
5 |
Significant
physical highway capacity additions carried out in the context of major
infrastructure renewal are appropriate only under certain conditions (use of
risk assessment here). |
6 |
Incident
management is essential to effective congestion management |
7 |
Corridor
protection and official street mapping are necessary to preserve options. |
The CDTC process departs from the traditional
approach to addressing travel needs.
CDTC strives first to maintain existing conditions and reduce the impact
of forecasted travel by implementing demand management programs before
considering capacity expansion; it uses the concept of risk assessment
and tradeoff analysis in designing projects; and it is taking a fresh
look at why travel occurs and why gridlock often does not.
The level of traffic congestion today in the
Capital District is generally acceptable, except on a few routes during peak
hours. However, CDTC forecasts a five-fold
increase in unacceptable delay by the year 2015 as the result of projected
development, a growth in both income and vehicle ownership, and shifts in the
geographic distribution of activity toward suburban and exurban areas. The number of critically congested corridors
is expected to increase from 14 (1990) to 33 (2015) if nothing happens to
mitigate the growth. The Congestion
Management System states that this “trend” will result in a congestion
condition that is a threat to the Capital District. The New Visions Transit Task Force
noted that this increased highway congestion will also hurt transit, as the
auto driver can take alternate routes while the bus rider is stuck in the
traffic.
CDTC intends to revise its CMS principles and its
identification of critical congestion corridors in the context of the New
Visions 2030 exercise. CDTC and NYSDOT
will work together to try to develop procedures for the "tradeoff
analysis" specified in CDTC's congestion
management principles. The tradeoff
analysis is required in considering capacity aspects of highway projects,
particularly infrastructure reconstruction projects. CDTC also remains committed to examining the
actual congestion relief benefits achieved from CMS projects.
Quantifying Congestion
In quantifying congestion, CDTC presently
uses STEP, its travel forecasting model (CDTC is in the process of switching to
VISUM). CDTC maintains a current traffic
count file containing all NYSDOT, CDTC and local machine and manual traffic
counts. Using NYSDOT’s
extensive traffic data collection program on the State highway system, CDTC has
been able to make a credible comparison of actual traffic growth relative to
its STEP model forecasts. The comparison
shows that the overall forecasts have been quite accurate. Because of the 1995 CMS was developed on
these forecasts, CDTC’s year-2000 corridor priorities
remain virtually unchanged. The long
development time for the major initiatives in the CMS has meant that the basic
policy set of the 1995 CMS also remains unchanged. For these reasons, the CDTC progressed
minimal maintenance of the CMS to date.
The most significant aspect of CDTC’s approach to CMS since 1995 is that the concept has
been, and continues to be, fleshed out.
CDTC is now rethinking the traditional approach to addressing forecasting
and addressing travel, and base on past performance, this endeavor should prove
interesting to the transportation community.
Identifying Congestion
Figure
13: Congestion at |
CDTC uses the concept of excess
delay to identify areas of congestion.
Excess delay is the amount of time spent at a given location that exceeds
the maximum amount of time that is generally considered acceptable. Table XXX-2 shows the excess delay threshold
values adopted by CDTC. For auto and
freight travel, excess delay is the amount of time spent at an intersection or
along a highway segment in Level-of-Service (LOS) E and F conditions that
exceed the maximum LOS D time. Thus, if
you sit in your automobile for more than 40 seconds waiting to go through an
intersection, you are experiencing congestion at that particular location.
Since the transportation user’s perception
of congestion is related to its magnitude and/or severity, CDTC has identified
those corridors that have significantly greater congestion than typical. These corridors are defined as contiguous
highway segments that, in aggregate, exceed certain thresholds. By far, the most critically congested
facility is the Adirondack Northway (I-87), having 1,263 excess person hours of
delay, as compared with the second most sever highway having 437 excess person
hours of delay. The threshold values
apply uniformly to auto, bus and freight transportation without additional
monitoring efforts.
Investment Decisions
The congestion management
principles in the CMS plan have had an increasing influence in regional
transportation decision-making. CMS,
however, is considered in the context of everything else, rather than the
driving force. In choosing projects to
be on the TIP, CDTC still does not entertain a stand-alone congestion project
unless it is on the critical CMS list.
If an infrastructure project is up for discussion, it has a better
chance of selection if it is also on the critical list.
The CMS plan established two main
goals for use in making investment decisions:
·
support the growth in economic
activity and quality of life by limiting the amount of excess delay; and
·
implement demand management programs first, before performing
capacity expansions.
Table 4: Excess Delay Threshold Values |
|
Facility
Type |
Excess
delay Threshold |
Intersection |
40
seconds of stopped delay |
Freeway |
1500
vehicles/lane, one direction/hour |
Multi-lane
Arterial w/median |
1400
vehicles/lane, one direction/hour |
Multi-lane
Arterial w/o median |
1250
vehicles/lane, one direction/hour |
Two-lane
Arterial and collector |
1000
vehicles/direction/hour |
Local
(residential) road |
625
vehicles/direction/hour |
Thus, the CDTC strategy for
reducing congestion is to employ a combination of TIP capital investments,
incident management, demand management strategies, access management
strategies, and operational measures. CDTC's TIP has a multi-year commitment to develop and
implement an Advanced Traffic Management System (ATMS) for the Capital
District. ITS is playing an
increasingly important role in the Capital District, including such measures as
the New York State Thruway Authority Electronic Toll Collection system (E-Z
Pass) and the joint NYSDOT/State Police Transportation Management Center.
As discussed in Section VI:
Transportation Improvement Program, candidate TIP projects go through a
three-step process: screening, evaluation of merits, and project
selection. During the screening process,
candidate projects must be determined to be consistent with the CMS
component. For projects specifically
targeted at congestion mitigation, it must have local community support, be
able to document that there does exist congestion (for highway capacity work),
and the project must include commitments to local land use management (in the
case of highway widening). These
criteria reinforce the regional planning process and assure that projects
evaluated for funding meet the CMS’ seven principles. The “Meeting an Identified Need” criteria for
mobility projects is a Level of Service of E or below, either under current
conditions or projected conditions in the year of programming, and must exist
in order for the project to be evaluated further.
Once the project successfully
passes through the screening process, it is assigned a detailed ranking based
on the merits of the project. Benefit to
cost ratios (b/c) are calculated by CDTC staff wherever possible. Five measures of project benefit are calculated: safety, travel time, energy/user, life cycle
and "other" benefits. The
cost benefits of proposed mobility improvements are measured by calculating
savings in user operating cost and travel time savings[i] that would result from
project implementation. Future year
traffic is assigned to the network with and without the proposed project. User operating costs and travel time costs
are calculated as the difference between the costs resulting from these two
assignments.
In making investment decisions on
capacity aspects of highway projects, particularly infrastructure
reconstruction projects, CDTC has adopted a CMS-driven design approach, wherein
any significant capacity additions carried out in the context of major
infrastructure renewal are appropriate only under compelling conditions. CDTC requires a tradeoff analysis inherent in
the concept of Risk Assessment that focuses on the opportunity cost of
selecting alternative designs. The next
section - Preservation of Existing Infrastructure - further details this
approach.
Managing Congestion on the System
While the trend line for vehicle
travel demand shows a potential VMT increase of 30% by the year 2015, CDTC is
committed to reducing the travel impact by one-third to one-half through travel
demand management efforts and land use strategies. Much of the reduction will be guided by the
principles and proposed actions contained in the CMS. Projects are designed for the traffic target,
not for the trend (note: consultants have found it somewhat disconcerting to
design for traffic less than projected).
CDTC’s approach appears to be working
well in practice, as the STEP Model forecasted an average annual growth rate
for PM peak-hour VMT of 2.5% for the 1990's, compared to the actual VMT on the
State touring routes of 1.9% during this period. Thus, the preliminary indication is that VMT
growth has on average been lower than forecast, hereby lending credibility to
the New Visions assumption that traffic growth could be dampened with
plan implementation. CDTC hopes that the
regional ITS deployment will help achieve the reduced VMT impact. An update and refinement of the regional ITS
program will be progressed for the New Visions 2030 effort.
New Look at
Accommodating Travel
The traditional approach to
transportation investment in general, and highway congestion in particular, has
been modified in the Capital District through its use of the concept of risk
management (see Section VIII: Preservation of Existing Infrastructure). CDTC, however, is embarked on a fundamental
reassessment of the principles and reasons why people travel, challenging
certain traditional assumptions.
For example, a traditional
approach to congestion is to identify present or future locations of congestion
and make improvements to achieve a certain Level of Service, the assumption
being that an improved LOS would be the choice of the public. However, the people of the Capital District
have expressed their opinion that congestion should not be looked at as the
sole measure of whether or not a highway improvement should be made. During the survey of residents along the
relatively congested Route 5 corridor, 79% said existing level of congestion
along on Route 5 would be acceptable if other services were improved (transit, pedestrian,
etc.). In other words, maintaining
the existing level of congestion was acceptable.
Another topic being looked at by CDTC that challenges the traditional understanding of travel is: Why doesn’t gridlock occur? CDTC found that its overall forecast of future travel was fairly accurate, but its forecasts in certain congested corridors where congestion was expected to increase were not realized. Mr. Poorman has speculated that personal and commercial travel behavior accounts for congestion through an equilibrium process that prevents gridlock.[ii] We note that The Brookings Institute has recently voiced similar speculations.[iii]
Mr. Poorman notes that certain congested
arterials in
When new capacity is added to the highway system, people
apparently tend to trade-in the travel timesaving benefit and move further out
to the suburbs for bigger homes or possibly better schools. Conversely, when an existing route becomes
congested, people make alternative travel choices. This apparent balancing effect leads to the
idea that, in a region like the Capital District, investments are a choice
– there is no “we have to do it”. The
choice is – where do we want the traffic and what physical condition do we want
the system to be in? CDTC staff will further explore
these issues.