- System and Use Characteristics
- Physical Conditions
- Pavement Condition
- Lane Width, Alignment, and Access Control
- Bridge Conditions
- Operational Performance
- Capital Investment Requirements
- Rural Interstates
- Urban Interstates
- Bridge Preservation
- Current Spending Versus Investment Requirements
Chapter 3 describes the physical conditions of highways throughout the United States. There are numerous ways to examine physical conditions. This section focuses on Interstate pavement condition, lane width, alignment adequacy, bridge deficiencies, and bridge age.
Exhibit 16-5 shows the percentage of total Interstate miles with "Acceptable" or better ride quality by function class for select years from 1995 to 2002. Exhibit 16-6 shows the percentage of Interstate pavement meeting a standard of "Good" ride quality. (Data for other functional systems can be found in Exhibit 3-14.) Since 1995, the number of Interstate miles rated as having "Good" ride quality has increased for all three population subsets of Interstate highways.
|Location of Interstates||1995||1997||1999||2000||2002|
|Small Urban Areas||94.4%||95.8%||95.4%||95.7%||95.3%|
|Location of Interstates||1995||1997||1999||2000||2002|
|Small Urban Areas||49.8%||51.4%||58.2%||61.6%||64.9%|
In 2002, rural area Interstates had the greatest percentage of miles with "Acceptable" or better ride quality. About 98 percent of rural area Interstates met this standard. As a subset of the miles with "Acceptable" ride quality, 71.9 percent of rural Interstate miles met standards required for classification as "Good" ride quality.
For small urban Interstate miles, 95.3 percent met the criteria for "Acceptable" ride quality. As a subset of the miles with "Acceptable" ride quality, 64.9 percent met the standards to be classified as "Good" ride quality in the year 2002.
|Q.||How has the percent of Interstate travel occurring on pavements with "Acceptable "and "Good" ride quality changed since 1995?|
As discussed in Chapter 3, another way to evaluate ride quality is to consider the vehicle miles traveled on routes with "Acceptable" or "Good" ride quality, rather than simply looking at the miles of pavement themselves (see Exhibit 3-15). On this basis, the percentage of rural Interstate travel on pavements with "Acceptable" ride quality rose from 94.5 percent in 1995 to 97.3 percent in 2002, while the percentage of travel on pavements with "Good" ride quality rose from 53.3 percent to 72.2 percent.
Conditions also improved for urbanized Interstates, as the percentage of travel on pavements with "Acceptable" ride quality rose from 88.8 percent to 89.3 percent, while the percentage of travel on pavements with "Good" ride quality rose from 39.1 percent to 43.8 percent.
For small Urban Interstates, performance was mixed, as the percentage of travel on pavements with "Acceptable" ride quality declined from 94.9 percent to 94.6 percent, while the percentage of travel on pavements with "Good" ride quality rose from 51.4 percent to 65.1 percent.
In 2002, 91.7 percent of urbanized Interstate miles met the criteria for "Acceptable" ride quality. As a subset of this group meeting "Acceptable" ride quality, 48.7 percent of the urbanized Interstate miles met the standards to be classified as having "Good" ride quality.
Lane Width, Alignment, and Access Control
As described in Chapter 3, roadway alignment affects the level of service and safety of the highway system. Inadequate alignment may result in speed reductions as well as impaired sight distance. In particular, trucks are affected by inadequate roadway alignment with regard to speed.
There are two types of alignment: horizontal (curvature) and vertical (gradient). Alignment adequacy is evaluated on a scale from Code 1 (best) to Code 4 (worst). Exhibit 16-7 summarizes alignment for rural Interstates (alignment is normally not an issue in urban areas). More than 93.3 percent of rural Interstate miles are classified as Code 1 for vertical and 95.7 percent are classified as Code 1 for horizontal alignment.
|Code 1:||All curves and grades meet appropriate design standards.||93.3%||95.7%|
|Code 2:||Some curves or grades are below design standards for new construction, but curves can be negotiated safely at prevailing speed limits. Truck speed is not substantially affected.||5.9%||1.1%|
|Code 3:||Infrequent curves or grades occur that impair sight distance or severely affect truck speeds. May have reduced speed limits.||0.3%||0.8%|
|Code 4:||Frequent grades occur that impair sight distance or severely affect truck speeds. Generally, curves are unsafe or uncomfortable at prevailing speed limit, or the speed limit is severely restricted due to the design speed limits of the curves.||0.5%||2.4%|
Lane width can have an impact on highway safety and operational performance. Currently, higher functional systems such as Interstates are expected to have 12-foot lanes. As shown in Exhibit 16-8, approximately 99.8 percent of rural Interstate miles and 98.5 percent of urban Interstate miles have minimum 12-foot lanes widths (see also Exhibits 3-19 and 3 20 in Chapter 3).
The vast majority of the Interstate mileage consists of divided highways with a minimum of four lanes and with full access control. The Interstate Systems for Alaska and Puerto Rico are not required to meet this standard. For Alaska and Puerto Rico, the requirement is that construction is adequate for current and probable future traffic demands and the needs of the locality. In Alaska, 1,034 miles of rural Interstate are not required to have a minimum of four lanes and full access control. For urban Interstates, 104 miles do not meet the specified criteria for access control; 53 of these miles are in Puerto Rico and the remaining miles are in Alaska.
Exhibit 3-33 in Chapter 3 identifies bridge deficiencies by functional system, while Exhibit 3-35 shows the percentage of rural and urban bridge deficiencies for the Interstate System in particular. Approximately 15.8 percent of all rural Interstate bridges were deficient in 2002, including 1,104 that were structurally deficient (about 4.0 percent of the total number) and 3,210 that were functionally obsolete (11.8 percent of the total number). Among rural functional systems, only other principal arterials had a lower percentage of bridge deficiencies.
About 26.3 percent of all urban Interstate bridges were deficient in 2002. This included 1,715 structurally deficient bridges (6.1 percent of total urban Interstate bridges), and 5,617 functionally obsolete bridges (20.1 percent of the total). Among urban functional systems, the Interstate System had the lowest percentage of deficient bridges.
The number of deficient bridges has steadily declined in recent years. In 1994, for example, 18.5 percent of rural Interstate bridges were deficient. That number has declined to 15.8 percent. The number of deficient urban Interstate bridges also declined, from 30.6 percent in 1994 to 26.3 percent.
The Federal Highway Administration also looks at bridge deficiencies by the percent of deficient deck area. Approximately 17.9 percent of the rural Interstate bridge deck area was deficient in 1996. This has decreased to 14.6 percent in 2002. This is the lowest percent deficient deck area for all rural functional classes.
The percent of deficient deck area on urban Interstate bridges was 34.2 percent in 1996. By 2002, this had decreased to 31.0 percent.