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Lane Design

Acceleration/Deccelearation Lane with Taper Only

Acceleration Lane

Standards

PennDOT: The combination of highway speeds, volumes, location and arrangement of driveways and intersections may require the installation of an acceleration lane to serve a proposed low, medium or high-volume driveway. A lane width of 14 feet is recommended where curbs exist and 12 feet where no curbs are in place.

Acceleration lanes are not recommended at driveways. The length of an acceleration lane is determined on an individual site basis and according to the amount of existing lot frontage. The storage length of an acceleration lane is typically between 150 and 250 feet. The length of the taper is usually between 75 and 150 feet. At un-signalized intersections with deceleration lanes, an acceleration taper is sometimes sufficient to allow vehicles to adjust their path of travel.

Comments

A speed-change lane should be sufficiently long and wide enough to enable a driver to maneuver a vehicle into it properly, and once in it, to make the necessary increase in speed.

Warrants for the use of speed-change lanes cannot be stated definitively. Many factors must be considered, such as speeds, grades, traffic volumes, capacity, type of highway, vehicle type, the arrangement and frequency of intersections, and accident experience. Observations and considerable experience with speed-change lanes have led to the following conclusions:

1. Speed-change lanes are warranted on high-speed and on high-volume highways where a change in speed is necessary for vehicles entering through-traffic lanes.
2. All drivers do not use speed-change lanes in the same manner; some use little of the available facility. As a whole, however, these lanes are used sufficiently to improve the overall safety and operation of the highway.
3. Use of speed-change lanes vary according to traffic volumes, the majority of drivers use them when traffic volumes are high.

Acceleration lanes have limited applicability, are improperly used and often become a place where cinders collect.

Recommendation

Provide additional right-of-way adjacent to acceleration or deceleration lanes to provide for future road widenings. The extended right-of-way needs to go a minimum of 5 feet beyond the existing width of the acceleration or deceleration lane.

Deceleration Lane

Designed Speed	Distance (feet*)
30 MPH	235
40 MPH	315
50 MPH	435

*Minimum distance on grades less than 2%.

Storage Length

Un-signalized Intersections/Driveways: Storage length is based on the number of turning vehicles likely to arrive in an average 2-minute period during the peak hour. Minimum space for at least one car and one truck with over 10 percent truck traffic should be provided, otherwise, space for two cars is sufficient.

Signalized Intersections/Driveways: The required storage length depends on the signal cycle length, the signal phasing and the rate of vehicular arrivals. It should probably be one and one-half to two times the average number of vehicles that would store per cycle, which is predicated on the design volume.

Comments

A speed-change lane should be sufficiently long and wide enough to enable a driver to maneuver a vehicle into it properly, and once in it, to make the necessary reduction in speed.

The issue of proximity to existing and prospective bus stop locations should be evaluated in the presence, design and placement of acceleration and deceleration lanes. On a case-by-case basis, PennDOT's Engineering District 6-0 has discouraged the use of deceleration lanes for bus stops where the volume of right turns is significant and there is a continuous or periodic free-flow condition. This is because of the potential of merge and weave-related crashes that could occur as curbed buses are leaving the bus stop and returning to the through-traffic flow, using the deceleration lane to accelerate.

The increased use of deceleration lanes has reduced SEPTA's ability to identify safe locations for bus stops that are within reasonable distance of trip generators. This is particularly true where multiple access points are proposed and/or where minimal sidewalk connections exist or are being proposed. As a general rule, development proposals and other projects that touch existing bus stops or that would support the installation of a new stop should be vetted with SEPTA early in the process, particularly if the new stop location is proposed to be sited in an acceleration or deceleration lane.

Many factors must be considered, such as speeds, traffic volumes, capacity, type of highway, vehicle type, the arrangement and frequency of intersections, and accident experience. Observations and considerable experience with speed change lanes have led to the following conclusions:

1. Speed-change lanes are warranted on high-speed and on high-volume highways where a change in speed is necessary for vehicles entering or leaving the through-traffic lanes.
2. All drivers do not use speed-change lanes in the same manner; some use little of the available facility. As a whole, however, these lanes are used sufficiently to improve the overall safety and operation of the highway.
3. Use of speed-change lanes varies according to traffic volumes, the majority of drivers use them when traffic volumes are high.
4. Long tapers enhance the function of speed change-lanes.
5. Deceleration lanes on the approaches to at-grade intersections that also function as storage lanes for turning traffic are particularly advantageous because they reduce hazards and increase capacity.

Recommendations

• Provide a deceleration lane into major subdivisions and commercial or office developments especially where no traffic control device exists and where conditions warrant.
• Provide a deceleration lane on principal arterial roads where only one through lane exists and where conditions warrant.
• PennDOT recommends a 14-foot wide deceleration lane for curbed areas.
• Provide additional right-of-way around acceleration or deceleration lanes to provide for future road widenings. The extended right-of-way needs to go a minimum of 5 feet beyond the existing width of the acceleration or deceleration lane.

Lane Width: Local and Internal Roadways

Lane widths should not be determined by only one factor, but according to the following: intended function of the road, expected traffic volume, intensity of adjacent land use, lot size, building setbacks, length of driveway, number of garages, parking needs, curbing, mailbox location, and overall neighborhood design.

While access is the primary function of all local roads, some local roads provide limited mobility functions. Local roads should have a sub-classification because of varied functions.

Primary Distributor: Section A

• Generally moves traffic to the arterial or collector networks from neighborhoods or subdivisions.
• May extend through a municipality and may serve an inter-municipal function, but it should not provide a regional function.
• Parking should be prohibited, except in urban or village areas, and the width of the road should accommodate speeds in the 25-45 MPH range, with daily traffic volumes between 750-2,500 vehicles.
• Parcel access should not be prohibited, but should be more limited than a secondary distributor or local access road.

Secondary Distributor: Sections B & C

• Extends through a neighborhood or subdivision, moving traffic to a primary distributor or directly to the collector network. Secondary distributors basically provide an intra-municipal function.
• On-street parking is not prohibited, but should be limited.
• The design of the road should accommodate travel speeds in the 15-25 MPH range, with daily traffic volumes between 200-1,500 vehicles.

Local Access Street: Sections D,E,F

• A local access street is strictly intended for access to adjacent properties.
• Traffic speeds should be less than 15 MPH and daily traffic volumes should be less than 500 vehicles.
• Other design features include: short length of road to discourage through traffic, smaller curb radii, driveway and alignment radii to preclude higher speeds.
• In a neighborhood of small lots with limited off-street parking, the cartway should be wider to accommodate on-street parking.

Local Access Street: Section G

• A narrow cartway should be provided in a neighborhood of large lots (cross-section G) which have off-street parking.

Local Access Street: Section H

• Local roads serving commercial, office and industrial developments.
• The width and number of travel lanes on local roads in a large non-residential development depends on the anticipated traffic volumes.

The function of local roads adjacent to or within a new development needs to be carefully considered. A road that is intended to serve as a local access street should be designed accordingly. If a road is intended to eventually connect into another subdivision or neighborhood, then it should be designed as a secondary distributor. Over-design of a local road can lead to wasted expense and higher housing costs and could impact the safety and residential quality of a neighborhood. Under-design can lead to safety problems and expensive reconstruction.

The width of a residential street should be based on its intended use, not on a "one-size-fits-all" standard. The ordinance requirements should link the design of the street to the anticipated number of trips on the street and whether or not on-street parking will be provided. Where smaller lots are proposed, on-street parking should be permitted on at least one side of the street. Benefits of appropriate street design include reduced impervious surface, lower maintenance costs, reduced width of the streetscape, and a reduction in speeding that is encouraged by wide roadways.

Recommendations

Primary Distributor Streets - The primary distributor street is the highest order of street that can be classified as residential and will carry the largest volume of traffic at higher speeds. This level of street is unsuitable for providing direct access to homes and such access should be avoided.

Primary distributor streets shall be required when the ADT anticipated on the street exceeds the limits for residential secondary distributor streets. If the anticipated ADT exceeds three thousand (3,000) the street shall be classified as a higher order than a primary distributor and the township, upon recommendation of their Engineer, shall determine the required design standards. On-street parking shall be prohibited on primary distributor streets. Primary distributor streets should be designed to have no residential lots fronting on them. However, in no case shall the percent of total length of the primary distributor street with residential frontage on and taking access from the street exceed the following:

Average Daily Trips (ADT) Level	Allowable Access Frontage Along Primary Distributor
1,000 to 1,199	20%
1,200 to 1,599	10%
1,600 to 1,999	5%
2,000+	0%

Travel lane widths shall be based upon anticipated average daily trips as follows. The wider of the two lane widths shall be used when raised curbs are proposed.

Average Daily Trips (ADT)	Travel Lane Width	Total Cartway Width
2,000 ADT or less	10 to 11 feet	20 to 22 feet
More than 2,000 ADT	11 to 12 feet	22 to 24 feet

Secondary Distributor Streets - The secondary distributor street is the middle order street in the residential street hierarchy. It carries more traffic than the local access street but can provide an acceptable if not optimum environment for a residential neighborhood. Each secondary distributor street shall be designed so that no section of it will convey a traffic volume greater than five hundred (500) ADT.

Design Parameters for Secondary Distributor Streets

Design Factors			Street Standards
	Parking
Development Type Fronting on Street	On-Lot	On-Street / Spillover	Travel Lane1 Width	Parking Lane Width	Total Cartway Width	Individual Driveway Acceess
Permanent open space, no residential frontage	None	None	10 to 11 feet	n/a	20 to 22 feet	n/a
Lots 2 acres2 or more, deed restricted against further subdivision	On-Lot	None	10 to 11 feet	n/a	20 to 22 feet	Yes
Lot widths 100 feet or greater	On-Lot	None	10 to 12 feet	n/a	20 to 24 feet	Yes
Lot widths 40 to 100 feet	On-Lot	One Side	11 to 12 feet	8 feet	38 to 32 feet	Yes
Lot widths less than 40 feet w/rear alley access	On-Lot from alley	Two Sides3	10 to 12 feet	16 feet (8 each side)	36 to 40 feet	No
Lot widths less than 40 feet or no separate housing lots (apartments)	On-Lot or off-street parking lot provided	Off-street parking lot provided	10 to 12 feet	n/a	20 to 24 feet	Yes (for parking lots)

1) If no curbing or flush curbing is being used, the minimum width should be used. If raised curbing is proposed, at least one additional foot of width above the minimum shown should be provided.
2) Performance Streets uses a minimum lot size of five acres.
3) A single parking lane may be provided if houses front on only one side of the street. In such cases, the total cartway width may be reduced by eight (8) feet to a width of 28 to 32 feet.

Local Access Streets - The local access street is the lowest order street in the residential street hierarchy. It is intended to carry the least amount of traffic at the lowest speed and will provide the safest and most desirable environment for a residential neighborhood. Developments should be designed so the maximum number of homes possible front on this class of street. A local access street shall be designed to carry no more traffic than is generated on the street itself. Each local access street shall be designed so that no section of the street carries an Average Daily Traffic (ADT) volume of greater than two hundred (200).

Design Parameters for Local Access Streets

Design Factors			Street Standards
	Parking
Development Type Fronting on Street	On-Lot	On-Street / Spillover	Travel Lane1 Width	Parking Lane Width	Total Cartway Width	Individual Driveway Acceess
Permanent open space, no residential frontage	None	None	8 to 9 feet	n/a	16 to 18 feet	n/a
Lots 2 acres2 or more, deed restricted against further subdivision	On-Lot	None	8 to 9 feet	n/a	16 to 18 feet	Yes
Lot widths 100 feet or greater	On-Lot	None	9 to 10 feet	n/a	18 to 20 feet	Yes
Lot widths 40 to 100 feet	On-Lot	One Side3	9 to 11 feet	8 feet	26 to 30 feet	Yes
Lot widths less than 40 feet w/rear alley access	On-Lot from alley	Two Sides4	9 to 11 feet	16 feet (8 each side)	34 to 38 feet	No
Lot widths less than 40 feet or no separate housing lots (apartments)	On-Lot or parking lot provided	Off-street parking lot provided	10 to 11 feet	n/a	20 to 22 feet	Yes (for parking lots)

1) If no curbing or flush curbing is being used, the minimum width should be used. If raised curbing is proposed, at least one additional foot of width above the minimum shown should be provided.
2) Performance Streets uses a minimum lot size of five acres.
3) Alternatively, for very low volume streets, two parking lanes and one travel lane can be provided (see "Local Access Street" F in Figure 3-3).
4) A single parking lane may be provided if houses front on only one side of the street. In such cases, the total cartway width may be reduced by eight (8) feet to a width of 26 to 30 feet.

Lane Width: Public Roadways

According to AASHTO, "No feature of a highway has a greater influence on the safety and comfort of driving than the width and condition of the surface." Lane widths of 10-13 feet are most common in Chester County, with 12-foot lanes predominant on most high-type highways. The County has been working with PennDOT to reduce lanes to 11 feet to improve shoulders for biking. Other research studies by the Federal Highway Administration have generally shown that the accident rates decrease with an increase in the width of the traffic lane.

AASHTO states that a 24-foot cartway is required to permit desired clearance between commercial vehicles. An effective width of 20 feet is considered adequate only for low volume roads where meetings and passings are infrequent and the proportion of trucks is low.

To qualify for financing through PennDOT's Liquid Fuels Tax Fund, roads must be at least 16 feet wide.

Most full-sized transit vehicles are 102 inches (8.5 feet) in width. When adding 1 foot on each side for protruding mirrors, this means that buses need 10.5 feet of clearance for operations. This means that arterials and collectors should be at least that wide if they currently or prospectively would carry transit vehicles in the course of their travels. This also includes any possible routes that would be used in the event of a detour caused either by a recurring or incident-related blockage.

Recommendations

Cartway widths should be flexible and site specific according to lot sizes, the desire or need for on-street parking, the functional classification of the road and overall design of the subdivision.

Local Access Streets

Roadway Design	All	Growth Area (including Landscapes2 Urban, Suburban Center and Suburban)
	Expressway	Major Arterial	Minor Arterial	Major Collector	Minor Collector	Local Road
Desired Operating Speed	55-65 MPH, 40 MPH minimum	30-55 MPH	25-55 MPH	25-55 MPH	25-30 MPH	20-25 MPH
Travel Lane	12'-14'	10' to 12' depending on number of lanes, bike lanes, shoulders, etc.			9'-11'	9'-11'
Shoulder	8'-10'	4'-6'(if no bike lane or parking) 8'-10' in suburban commerical contexts			4'-6'(if no bike lane or parking)
Parking Lane (7'-8' parallel)	Prohibited	Recommended in urban landscape; evaluate feasibility in suburban (7'-8' parallel)

Roadway Design	All	Rural Area (including Landscapes2 Rural, Agricultural, Natural and Village Centers)
	Expressway	Major Arterial	Minor Arterial	Major Collector	Minor Collector	Local Road
Desired Operating Speed	55-65 MPH, 40 MPH minimum	45-55 MPH	35-55 MPH	35-55 MPH	20-35 MPH	20-30 MPH
Travel Lane	12'-14'	11' to 12' depending on number of lanes, bike lanes, shoulders, etc.			10'-11'	9'-11'
Shoulder	8'-10'	8'-10'	8'-10'	4'-8'	4'-8'	2'-8'
Parking Lane (7'-8' parallel)	Prohibited	n/a	n/a	n/a	n/a	n/a

Left-Turn Lanes

Standards

PennDOT: Please refer to the section 11.16 of the PennDOT, Traffic Engineering Manual, Publication 46

Comments

For signalized intersections a Level of Service analysis will determine the need for a left-turn lane. The Federal Highway Administration found that channelization of intersections produces an average 32.4 percent reduction in all types of accidents. Accidents involving personal injuries decreased by over 50 percent.

Recommendations

Left-turn lanes should be provided at new and existing driveways and intersections that exhibit the following conditions:

1. medium-volume (750+ADT) driveways and roads which intersect arterial and collector roads in rural areas;
2. high-volume (1500+ADT) driveways or roads that intersect arterials;
3. driveways on the crest of a hill where sight distance is limited; and
4. intersections where sight distance is limited due to a horizontal and/or vertical curve.

In addition to these four conditions , left-turn lanes should be provided where warrants are met based on the recommendations of the section 11.16 of the PennDOT, Traffic Engineering Manual, Publication 46

Number of Travel Lanes

The number of lanes is determined by capacity analysis for selected levels of service. This determination is based on factors such as: traffic volumes; number of trucks, turning movements, grades, parking requirements, and signal timing, etc.

On residential streets, at least one moving lane must be provided even where parking occurs on both sides. The level of user inconvenience on low-density, residential streets with one moving lane is low in areas where single-family units prevail.

Recommendation

Recommend use of the Transportation Research Board's, Highway Capacity Manual to determine the correct number of travel lanes for roads and intersections.

Shoulders

FHWA studies have generally shown that accident rates are reduced as shoulder width increases. Shoulders have many advantages such as:

• providing an emergency area, a maintenance and snow removal area and a space for bicycle and pedestrian use as well as overall structural support for the pavement;
• improving sight distances, capacity and maintaining uniform speeds, thereby increasing safety;
• providing an area to escape potential accidents or reduce their severity;
• giving the driver a sense of openness contributing to driving ease and freedom from strain; and,
• discharging stormwater from the pavement.

Recommendations

Local access streets in low-density areas do not require a paved shoulder. A graded, stabilized grass area which provides groundwater recharge is sufficient on these roads.

Public Roadway Shoulder Widths

	Growth Area	Rural Area
Expressway	8'-10'	8'-10'
Principal Arterial	4'-6' if no parking or bike lane; 8'-10' in suburban commercial contexts	4'-8'
Minor Arterial		8'-10'
Major Collector		4'-8'
Minor Collector	4'-6' if no parking or bike lane	4'-8'
Local Road	n/a	2'-8'

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