CE562 Lecture 12 Cross Section Elements 3

1. CE562 Lecture 12 Cross Section Elements (3) Text: A Policy on Geometric Design, pp. 305-375

2. Noise Control General consideration Noise is an unwanted sound. A highway designer should evaluate the probable noise level and consider means to reduce the noise if needed. The unit of noise is decibel (dB). Increase in noise by 10 dB makes impression of doubling the noise. A doubling in the sound intensity (acoustic energy) increases the noise by 3 dB. Noise decreases by 3-4.5 dB with doubling of distance from a highway. General Design Procedure 1. Define noise-sensitive areas along highway, 2. Determine criteria for noise impact, 3. Measure current noise level (prior highway construction), 4. Predict the noise level expected after highway is constructed, 5. Evaluate the noise impact, 6. Design countermeasures if needed.

4. Noise Control Predicting noise level The noise level should be predicted for the worst traffic hour for a typical day. The following factors should be considered: traffic characteristics (speed, volume, and compositions) topography (vegetation, barriers, distance) roadway characteristics (configuration, pavement type, grades, type of facility) Design countermeasures highway relocation depressed highway sections earth berms noise barriers (concrete, wood, metal, masonry walls) shrubs and trees

23. TunnelsGeneral Considerations and Types The following conditions may warrant tunnel construction long, narrow terrain ridges larger and complex intersections or sequence of major intersections on an irregular or diagonal street pattern railroad yards, airports and runways, or similar facilities parks or other land uses costly right-of-way acquisition Types of tunnels constructed by mining methods (horse-shoe or circular) constructed by cut-and-cover methods (rectangular) or hard-rock tunneling soft-ground tunneling

24. TunnelsDesign Considerations Tunnels create discomfort (feeling of confinement and traffic noise) and are expensive. Tunnels should be: as short as possible designed on tangents if possible graded with consideration of drivers comfort and construction cost ventilated and lighted The standards for alignment on open sections apply to tunnels with exception that the minimum requirements should be considered to minimize costs.

30. Ted Williams Tunnel � Boston�BIG DIG� The Ted Williams Tunnel will be carrying more than 90,000 vehicles a day.

37. Pedestrian Crossings and Ramps Pedestrian overcrossings and underscrossings are warranted when: peak pedestrian volume is heavy and vehicular traffic is moderate or heavy (CBDs, factories, schools), or abnormal hazard or inconvenience for pedestrians takes place (cross streets terminated by freeways or expressways). Design rules: Overpassings should be consider before underpassings is considered (less expensive, preferable by pedestrians), Fences near pedestrian separations prevent at-grade highway crossing, All pedestrian separations should have ramps; stairways can be provided in addition, Minimum width of walkways is 2.4 m, Screens are recommended on overpassings where dropping objects on the traveled way is the concern (near schools, playgrounds, not frequently patrolled by police), Continuous vision through the underpass reduces pedestrians discomfort.

39. Bus Turnouts Bus turnouts remove the bus from the traffic lanes. Freeways Bus turnout includes: deceleration section standing section acceleration section separation between bus lane and through lanes passenger platform pedestrian separation (overpass, ramps, stairs) signs and markings Arterials Bus turnouts should be considered where possible. They include: deceleration lane or taper (minimum 5:1) loading area (3-3.6 m wide and 15 m long for each bus) merging (reentry) taper (minimum 3:1)

42. Park and Ride Park-and-ride facilities offer convenient transfer from the passenger car (or bicycle) to public transit vehicles (bus, city train, underground). Location Adjacent to the street or highway Visible to the commuters Preceding the bottleneck Close to the residential area Design Elements of park-and-ride facility: long-term parking lot short-term parking lot bicycle parking passenger pickup and dropoff passenger shelters bus (train) loading and unloading areas taxi service bus roadways lighting and drainage

45. On-Street ParkingUse Curb-parking should be prohibited on freeways and major arterials Recommended on minor arterials, collectors and local roads located in developed areas Parallel parking preferred over angle parking (performance of through lanes and safety)

46. On-Street ParkingDesign Rules Arterials Minimum width of parking lane is 2.4 m (recommended width is 3.0-3.6), Minimum width of parking lane with adjacent bicycle route is 3.0-3.6 m. Urban collectors Minimum width of parking lane is 2.4 m (recommended width is 3.0-3.6), Minimum width of parking lane with adjacent bicycle route is 3.0-3.6 m, In residential areas, 10.8 m two-lane two-way traveled ways are sufficient (2.1 m parking lanes and 3.3 m through lanes). Local streets In residential areas 7.8 m traveled ways are sufficient for two-way traffic. Parking lanes should end 6.0 m in advance of the intersections.