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| [ 作者： | 来源： | 时间：2006-1-22 13:18:19 ] |
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- Categorical Exclusion
- Examples of categorical exclusions are actions which, based on past experience with similar actions, do not involve significant environmental impacts. They are actions which do not do any of the following: induce significant impacts to planned growth or land use for the area; require the relocation of significant numbers of people; have a significant impact on any natural, cultural, recreational, historic or other resource; involve significant air, noise, or water quality impacts; have significant impacts on travel patterns; or otherwise, either individually or cumulatively, have any significant environmental impacts.
- Central Business District (CBD)
- The downtown retail trade and commercial area of a city or an area having high land values, traffic flow, and concentration of retail business offices, entertainment, lodging, and services.
- Changeable Message Sign (CMS)
- A CMS is used to advise drivers of traffic or roadway conditions ahead and, in some cases, recommend alternate routes. The CMS also reduces driver frustration by providing advance warning. A CMS is also referred to as a Variable Message Sign (VMS).
- Collector Distributor (CD)
- A CD freeway system separates local and through traffic by use of CD roadways and through roadways ("main lanes" or "core roadway"). The CD roadway is located between the main lanes and a frontage road or local street system. On the main lanes, traffic flow is improved since weaving is eliminated and access points are reduced; the CD roadway provides needed freeway access points. A CD roadway is different from a frontage road because access to adjacent properties is not permitted. A CD roadway can complement an existing frontage road system by inclusion of ramps connecting the CD roadway to the frontage road; the frontage road is then better able to handle traffic accessing adjacent properties. For traffic traveling between a freeway system and more distant points, "direct connect" ramps can be used to "directly connect" the CD roadway to major thoroughfares (leading to major traffic generation areas) and, thereby, bypass frontage roads or local streets adjacent to the freeway. This CD roadway and direct connect ramp arrangement eliminates merging and weaving movements that would otherwise occur between the freeway, frontage road, and local roads. During peak traffic, this arrangement can provide the added benefit of keeping open those sections of freeway lanes approaching exit ramps since greater storage length for exiting traffic queues (lines of vehicles waiting their turn) is made; increased queue storage is made by the greater length of the direct connect ramps, the reduction of turbulence in the queue (no access to adjacent property), and the relocation of the queue away from, instead of parallel with the freeway. A CD system with direct connect ramps can promote intermodalism since it provides for easier movement of transit vehicles like buses. Buses can easily travel directly between the CD roadway and local streets without having to merge and weave on and off of frontage roads. The CD roadway's operating speed is generally lower than the main lanes since the CD roadway has more entrance and exit areas. It is worth noting that a freeway's optimal traffic carrying capacity occurs at around 45 mph. Because of this lower operating speed, the CD roadway may be designed with a lower design speed which allows for more flexible design. In general, a freeway system with high traffic volumes, in a city-type area, can have its overall traffic carrying capacity and flow operations improved by use of a CD system. CD systems are currently in operation in several cities across the nation.
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