Thursday, October 30, 2008

Pavement Maintenance

Hawaii at 0.39, had the second lowest score in the nation in Interstate Pavement Serviceability in 2004. The average score of Pavement Serviceability in the U.S was 0.82. The situation is even worse for Honolulu.

Pavement Serviceability Index or PSI is a standard pavement quality metric ranging from one (1) excellent to zero (0) for terrible. In 2006, for 66 urban areas with population of 500,000 or more:

• Los Angeles had the lowest average score of 0.16 and San Francisco-Oakland with next lowest score of 0.17. Honolulu and San Jose had the third lowest score of 0.19.
• There were 25 urban areas within the score range of 0.25 to 0.50 including Albuquerque with a score of 0.39.
• There were 29 urban areas within the score range of 0.51 to 0.75 including Salt Lake City with a score of 0.59.
• There were nine urban areas within the score range of 0.76 to 0.87 including Jacksonville with a score of 0.86 and Tampa-St. Petersburg with the highest score of 0.87.

As much as a 71% saving can be realized if preventive maintenance were performed in a systematic way. The core of PMS is rating the pavement surface quality for every street in the city. From that the system recommends a program of annual expenditures that will help maintain good quality streets at that level or higher by preventing or reducing the wear from weather and vehicles.

To keep a road in good condition its surface needs to be maintained. Failure to maintain the surface leads to failure of the entire layer of pavement and sometimes the subsurface base, forcing the replacement of the entire pavement layer with new asphalt – an expensive process. An easy way to think of pavement (asphalt) preservation is to liken it to changing engine oil in your car. If you change the oil on reasonable recommended schedule, generally, the engine will last a long time. The same goes for a properly built street – with a refresher coat every 7-10 years it will last twice as long as normal.

Breaks in the surface can lead to hairline crack formation which allows the entrance of water into and below the pavement, leading to a shortened pavement life and early failure of the pavement subgrade base. Seal coating restores the oxidized surface and seals the pavement to prevent water entrance as well as adding a new wear course and adding improved traction.

Seal coats such as chip seals are more environmentally sound than paving. Three applications of chip seals over a 30 year period will use less than half the rock and oil of a conventional asphalt overlay.

One mile of collector arterial can be chip sealed in one week. If it had been repaved, it would have taken one month. Sweeping of loose gravel begins immediately after the chip is laid down eliminating the need to close the road to traffic. A final top coat of light oil is placed on the chip a few days after the chip is laid down, locking down any remaining loose chips.

Repaving of a typical residential street with three inches of pavement, in 2008 dollars, runs the range of $25 – 35/square yard, depending on the complexity of the project. In comparison, chip seal runs $3-3.50/square yard. In a 30 year life cycle (assuming three chip seals) that translates to as much as a 71% savings. Savings sorely needed to rebuilt streets that have failed, improve substandard width streets, put in sidewalks and take care of aging traffic signals.

Maintenance and rehabilitation can be cheaper if performed early and methodically instead of lately and on a random, ad hoc or “plotical whim” basis. For example, Orange County, California implemented a Pavement Management System (PaMS) two decades ago. Before its implementation, 50% of the pavements in the network were in good condition and 24% in bad condition; while twenty years later 78% were in good condition and 5% in bad condition, while at the same time both funding and personnel in maintenance decreased (Allen and Lorick, 2007). Additionally, the Michigan Department of Transportation has calculated that savings in maintenance are $6 for every dollar invested in Pavement Management (National Cooperative Highway Research Program, 2004).

The sketch below clearly shows the deterioration of pavement condition over time.

Pavement Management “involves the identification of optimum strategies at various management levels as well as the implementation of these strategies. It is an all-encompassing process that covers all those activities involved in providing and maintaining pavements at an adequate level of service. These range from initial information acquisition to the planning, programming and execution of new construction maintenance, and rehabilitation, to the details of individual project design and construction; to periodic monitoring of pavements in-service”.

Pavement Management may use a large number of measurements for distresses in asphalt pavements: Alligator Cracking, Bleeding, Block Cracking, Bumps and Sags, Corrugation, Depression, Edge Cracking, Joint Reflection Cracking, Lane/Shoulder Drop-Off, Longitudinal and Transverse Cracking, Patching and Utility Cut Patching, Polished Aggregate, Potholes, Railroad Crossing, Rutting, Shoving, Slippage Cracking, Swell, Weathering and Raveling.

Pavement Management has been successful on many occasions, e.g., in the Arizona Department of Transportation (ADOT) which has used a PaMS since 1980. The ADOT found out that the roads after PaMS implementation deteriorate later than prior to its implementation. The Tolerable Roughness Level (93in/mi) at 16.8 years of age, instead of the 14.8 years they used to last before reaching that level prior to the implementation of PaMS. In the case of the Interstate Roads of the State of Arizona, the pavements last 31.6 years within the Tolerable Roughness Level once the PaMS was implemented and before PaMS they reached that level at 18.9 years of age. The savings in budget provided by PaMS in Arizona are estimated to be up to $423 million during the 16 year period that last from 1981 to 1996. The benefit/cost ratio procured by PaMS is 51 to 1.