What is congestion?

Virtually everyone who has ever traveled America’s roadways, whether it be in their own personal automobile, on a bus, or behind the wheel of a big rig, has had the experience of sitting in traffic.  Congestion is the level at which transportation system performance is no longer acceptable due to traffic interference. The level of acceptable performance can vary by the type of transportation facility, by location within the region, and by time of day. For instance, commuters typically expect and are generally willing to accept a certain amount of traffic during morning and evening “rush hours”. However, they may not be willing to accept that same level of performance in the middle of the day.

In general, highway congestion results when traffic demand approaches or exceeds the available capacity of the highway system. The level of traffic demand can vary significantly depending on the season, the day of the week, and the time of day. Also, the capacity of the highway system, which is usually thought of as constant, can change because of weather, work zones, traffic incidents, or other non-recurring events.

What is a Congestion Management Process (CMP)?

Federal transportation legislation (SAFETEA-LU) requires that each metropolitan planning area in the United States have what is called a Congestion Management Process, or CMP.  The CMP is a regional program to address and manage congestion within the 10-county Southwestern Pennsylvania region in order to facilitate the movement of people and goods.

The CMP is a broad, regional level planning tool designed to help manage congestion by identifying congested corridors and recommending multimodal strategies for congestion mitigation. The goal of the CMP is to provide information that helps transportation planners, professionals and others to understand the overall congestion climate in individual corridors and the region. Data on the congestion climate helps SPC, in partnership with other agencies, to formulate congestion management strategies. Data and information from the CMP benefits the transportation planning process by helping the region focus limited federal transportation dollars where they can have the greatest impact.

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How does the CMP work?

One of the main requirements of a CMP is the establishment of a coordinated program for data collection and system performance to define the extent and duration of congestion. SPC’s CMP includes a monitoring program that measures travel time and delay on approximately 100 roadway corridors in Southwestern Pennsylvania that currently experience congestion or serve growth areas that are likely to experience future congestion.  Data is collected by a vehicle traveling along with traffic during morning and evening peak hours, which are typically times with the highest amounts of congestion.  This data is analyzed in order to get a quantitative measurement of congestion in each corridor.  Once this data is analyzed, it is reviewed in consultation with other agencies and members of the community to compare and validate the patterns of congestion and identify sources of congestion.

The final data is then used to help assess various strategies for managing congestion.  The region’s transportation agencies and municipal governments then look for ways to implement appropriate strategies into on-going or new projects in those corridors.  Once strategies are implemented, a follow-up assessment is often conducted to determine the effectiveness of the improvements.

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What is being measured?

The CMP measures travel times between defined points in each corridor called nodes.  These travel times are compared to the amount of time it would take to traverse a given roadway segment at the posted speed limit if there were no interference. The difference between the ideal travel time and the actual measured travel time is referred to as delay.  The two basic measures of travel time and delay can be used to calculate a variety of performance measures including Delay per Vehicle, Delay per Vehicle per Mile, Total Delay, and Total Delay per Mile.  ThePerformance Measures section of this website provides more details about how these measures are calculated.  This information can also be found in the Glossary.

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How often is this data collected?

Because SPC’s CMP network is so extensive, it takes approximately 3 years to gather data on all the corridors in the network, so each corridor is measured about once every 3 years.  As the CMP network evolves, this data collection schedule may be adjusted in order to gather data on certain corridors more frequently and others less frequently.

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What is not measured?

The CMP is designed to measure what is called recurring congestion; that is, normal, everyday congestion that you would experience on a “typical day”. The CMP does not measure non-recurring congestion, which can be caused by special event traffic, traffic accidents, construction or other short-term or temporary occurrences. The CMP does not yet measure non-recurring congestion. SPC hopes to integrate non-recurring congestion measures at a later date. The charts below illustrate the type of recurring congestion that is being measured in the CMP and the type of non-recurring congestion that is not measured in the CMP.

As shown in Figures 1 and 2, traffic volumes typically follow recurring patterns.  In the SPC region, these patterns generally include morning peak hours between 7:00 and 9:00 a.m. and afternoon peak hours between 4:00 and 6:00 p.m.  SPC follows standard traffic engineering practice by conducting all of its CMP travel time runs during peak hours on Tuesdays, Wednesdays, and Thursdays to avoid potential anomalies that can occur on Mondays and Fridays.  Figure 3 illustrates an example of traffic patterns in a non-typical week, in this case Memorial Day week.  SPC avoids conducting travel time runs in weeks with holidays and other events like this that could skew traffic patterns.

Figure 1 - Typical monthly traffic volume patterns.

Figure 2 - Typical weekly traffic volume patterns.

Figure 3 - Non-typical weekly traffic volume patterns.

Figures 4 and 5 illustrate an example of non-recurring congestion, which SPC’s CMP does not measure.  Figure 4 shows typical spot speeds on the southbound side of the Veteran’s Bridge in Pittsburgh.  As Figure 5 shows, two incidents the week of August 22 – 28, 2005 caused significant congestion.  One of these incidents was a scheduled event at Mellon Arena which impacted the AM peak rush hour.  The second incident occurred during the Friday PM peak.  This could have been the result of very heavy traffic volumes, a traffic accident, or another incident.

Figure 4 - Typical weekly spot speeds.

Figure 5 - Non-typical weekly spot speeds.

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What can be done about non-recurring congestion?

Non-recurring congestion is caused by temporary disruptions, usually caused by traffic incidents (ranging from disabled vehicles to major crashes), work zones, weather, and special events. As they are frequently unexpected, and in many cases, unpredictable, non-recurring events can dramatically reduce available capacity and reliability of the entire transportation system. Therefore, measuring and dealing with non-recurring congestion can, by its nature, be very difficult since often you can not predict when and where it will occur.   The management of non-recurring congestion has received increased attention in recent years, primarily due to the recognition that it often causes more severe problems beyond recurring congestion.

While SPC’s CMP does not currently measure non-recurring congestion, there are regional strategies that help address non-recurring congestion. These strategies include incident management, special event planning, and road weather and work zone management. You can find out more about these in the Congestion Management Strategies and Monitoring Strategy Effectiveness portions of this website. SPC & PennDOT have also developed a Regional Operations Plan (ROP) (PDF, 1.65 MB) to help address non-recurring congestion.

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Where can I find out which corridors are included in SPC’s Congestion Management Process?

Check out the System Definition section of this website.

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Where can I find the detailed corridor data collected through SPC’s Congestion Management Process?

Check out the Performance Monitoring & Data section of this website.

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Español

Proceso de gestión de congestionamientos (CMP, por sus siglas en inglés)

El CMP es una herramienta de planificación diseñada para la gestión de congestionamientos, identificar corredores de tráfico intenso y evaluar estrategias multimodales, cuyo fin es mitigar la cogestión. Los datos provenientes del CMO también pueden ayudar a beneficiar el proceso de planificación, ayudando a la región a concentrar  los recursos federales limitados en áreas dónde podrán tener mejor impacto.

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Français

Procédure de gestion des embouteillages (CMP)

La CMP est un outil de planification visant à aider à gérer les embouteillages en identifiant les couloirs congestionnés et en évaluant les stratégies multimodales pour réduire les embouteillages. Les données de la CMP peuvent également être bénéfiques pour le processus de planification en aidant la région à concentrer les ressources fédérales limitées en budget là où elles peuvent avoir l'impact le plus important.

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SPC fournira libres traductions de documents essentiels par requête. Ce document est disponible en formats alternatifs sur demande. Veuillez  appeler le (412) 391-5590 pour plus d'informations.

La SPC s'engage à se mettre en conformité avec les exigences de non-discrimination des statuts de droits civils applicables, les décrets, les règlements et les politiques.  Sur avis préalable, l'hébergement peut être fourni à ceux qui ont des besoins particuliers liés à la langue, à la vue ou à l'audition. Si vous avez des besoins particuliers, n’hésitez pas à nous en faire part, ou si vous désirez de plus amples informations, veuillez contacter Matt Pavlosky au (412) 391-5590, poste 361 ou mpavlosky@spcregion.org.

Deutsch

Congestion Management Process (CMP)

Das CMP ist ein Planungswerkzeug, das entworfen wurde, um Stauungen zu managen, indem verstopfte Korridore bestimmt und multi-modale Strategien für Stauverringerung bewertet werden. Informationen aus dem  CMP  können auch für den Planungsprozess von Nutzen sein, indem sie helfen, die begrenzten Bundesmittel dort einzusetzen, wo siedie größte Wirkung erzielen.

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SPC bieten kostenlose Übersetzungen von wichtigen Dokumenten durch Anforderung. Dieses Dokument ist auf Anfrage in anderen Formaten erhältlich. Rufen Sie bitte (412) 391-5590 für weitere Informationen an.

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Italiano

Processo di gestione della congestione (CMP)

Il CMP è uno strumento di pianifica che ha lo scopo di contribuire a gestire la congestione, identificando i corridoi congestionati e valutando le strategie multi-modali per la mitigazione della congestione. I dati del CMP possono anche essere vantaggiosi per il processo di pianifica, aiutando la regione a concentrare i limitati dollari federali laddove hanno l’impatto maggiore.

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SPC fornirà libere traduzioni di documenti vitale da richiesta. Su richiesta, questo documento è disponibile in altri formati. Per ulteriori informazioni, si prega di chiamare il numero (412) 391-5590.

’SPC si impegna a rispettare i requisiti di eguaglianza dei diritti civili, degli statuti, degli ordini esecutivi, delle regolamentazioni e delle politiche applicabili. Se richieste in anticipo, possono essere accomodate le necessità particolari collegate alla lingua, alla vista o all’udito. Per richiedere sistemazioni speciali, inviare un commento o altre informazioni, si prega di contattare Matt Pavlosky al numero (412) 391-5590, interno 361 o all'indirizzo e-mail mpavlosky@spcregion.org.

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For more information about our Congestion Management Process, contact Doug Smith at (412) 391-5590 x327 or e-mail dsmith@spcregion.org.

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