Access Management Manual: Number, Location, and Spacing of Access Connections

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Section 3: Number, Location, and Spacing of Access Connections

Overview

The access connection distances in the following subsections are based on stopping sight distance and are intended for passenger cars on a level grade. These distances may be increased for downgrades, truck traffic, or where otherwise indicated for the specific circumstances of the site and the roadway. In other cases, shorter distances may be appropriate to provide reasonable access, and such decisions should be based on safety and operational factors supported by an engineering study.

Figure 2-1. Access Connection Spacing Diagram

Conditions for granting access to the state highway system will be stated in the access permit. Violation of the conditions under which the permit was granted, as determined by the Department, may require reevaluation of the access by TxDOT.

Where topography or other existing conditions make it inappropriate or not feasible to conform to the connection spacing intervals, the location of reasonable access will be determined with consideration given to topography, established property ownerships, unique physical limitations, and/or physical design constraints. The selected location should serve as many properties and interests as possible to reduce the need for additional direct access to the highway. In selecting locations for full movement intersections, preference will be given to public roadways that are on local thoroughfare plans.

In the absence of any safety or operational problems, additional access connections may be considered. Any additional access must not interfere with the location, planning, and operation of the public street system. Where the property abuts or has primary access to a lesser function road, to an internal street system, or by means of dedicated access easement, any access to the state highway will be considered as an additional access.

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New Highways on New Alignments (New Location)

When a new highway is constructed on a new alignment (new location), and the Commission designates that the new highway will be access controlled, direct access to the new highway will be determined prior to right-of-way acquisition and will be described in the right-of-way deeds.

Such new highways may initially have at-grade intersections, yet be intended for ultimate upgrade to full freeway criteria. In such cases, temporary access may be permitted where a property would otherwise be landlocked. When temporary access is permitted, the access permit will clearly state that the connection is temporary and will identify the terms and conditions of its temporary use and the conditions of the permanent access connection. The permit will also clearly state that the temporary connection will be closed and removed at such time that permanent access becomes available.

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Freeway Mainlanes

Freeways are intended to provide a very high degree of mobility. Accordingly, freeway mainlanes provide no direct access to property and access to the freeway mainlanes is provided only at interchanges and ramps. The spacing of interchanges and ramps needs to allow entering and exiting vehicles to weave safely and to provide adequate acceleration/deceleration.

The design of freeways is governed by the TxDOT Roadway Design Manual, Chapter 3.

Frontage Roads

Frontage roads are roadways that are constructed generally parallel to a freeway or other highway. Figure 2-2 shows a typical frontage road application. Freeway frontage roads normally have at-grade interchanges with the arterial streets, which are generally perpendicular to the freeway and are grade-separated from the freeway mainlanes. Under fully developed conditions, the at-grade intersections of frontage roads and arterials are typically signalized.

Ramps provide connections between the frontage roads and the freeway. Traffic traveling from an arterial street to the freeway first turns from the arterial onto the frontage road and then travels along the frontage road to a freeway entrance ramp. Traffic traveling from the freeway to an arterial street leaves the freeway by means of an exit ramp that connects to the frontage road and then travels along the frontage road to its intersection with the arterial street.

Direct access to the frontage road is prohibited in the vicinity of ramp connections, as described in the TxDOT Roadway Design Manual, Chapter 3.

Other streets may also intersect with frontage roads. By means of these intersections, access is provided between the freeway system and the developments that have access onto these streets.

Figure 2-2. Freeway with Frontage Roads

Frontage roads may be considered in order to provide direct access to abutting property where 1) alternative access is not available and the property would otherwise be landlocked, 2) it is not feasible for the Department to purchase the access, or 3) the frontage road allows for improved mobility together with the property access.

Table 2-1 gives the minimum connection spacing criteria for frontage roads. However, a lesser connection spacing than set forth in this document may be allowed without variance in the situations described in Chapter 2, Section 5.

It should be noted that for areas with conventional diamond ramp patterns, where an exit ramp is just prior to the arterial street, the most critical areas for operations are between the exit ramp and the arterial street and between the arterial street and the entrance ramp. In X-ramp configurations, where the exit ramp is just after the arterial street, the most critical areas are between the exit ramp and the subsequent entrance ramp. While Table 2-1 gives minimum connection spacing criteria, the critical areas with respect to the ramp pattern may need greater spacing requirements for operational, safety, and weaving efficiencies.

The distance between access connections is measured along the edge of the traveled way from the closest edge of pavement of the first access connection to the closest edge of pavement of the second access connection (Refer to Figure 2-1). Additionally, the access connection spacing in the proximity of frontage road U-turn lanes will be measured from the inside edge of the U-turn lane to the closest edge of the first access connection (Refer to Figure 2-3).

Figure 2-3. Frontage Road U-Turn Spacing Diagram

Anchor: #i999806Table 2-1: Frontage Road Connection Spacing Criteria
Minimum Connection Spacing Criteria for Frontage Roads ⁽¹⁾⁽²⁾
	Minimum Connection Spacing (feet)
Posted Speed (mph)	One-Way Frontage Roads	Two-Way Frontage Roads
< 30	200	200
35	250	300
40	305	360
45	360	435
> 50	425	510
(1) Distances are for passenger cars on level grade. These distances may be adjusted for downgrades and/or significant truck traffic. Where present or projected traffic operations indicate specific needs, consideration may be given to intersection sight distance and operational gap acceptance measurement adjustments. (2) When these values are not attainable, refer to the variance process as described in Chapter 2, Section 5.

Other State System Highways

This section applies to all state highway system routes that are not new highways on new alignments, freeway mainlanes, or frontage roads.

Table 2-2 provides minimum connection spacing criteria for other state system highways. However, a lesser connection spacing than set forth in this document may be allowed without variance in the situations described in Chapter 2, Section 5.

Table 2-2 does not apply to rural highways outside of metropolitan planning organization boundaries where there is little, if any, potential for development with current ADT volumes below 2000. For those highways, access location and design will be evaluated based on safety and traffic operation considerations. Such considerations may include traffic volumes, posted speed, turning volumes, presence or absence of shoulders, and roadway geometrics.

Anchor: #i1000396Table 2-2: Other State Highways Connection Spacing Criteria
Other State Highways Minimum Connection Spacing ^(1)(2)(3)
Posted Speed (mph)	Distance (ft)
< 30	200
35	250
40	305
45	360
> 50	425
(1) Distances are for passenger cars on level grade. These distances may be adjusted for downgrades and/or significant truck traffic. Where present or projected traffic operations indicate specific needs, consideration may be given to intersection sight distance and operational gap acceptance measurement adjustments. (2) When these values are not attainable, refer to the variance process as described in Chapter 2, Section 5. (3) Access spacing values shown in this table do not apply to rural highways outside of metropolitan planning organization boundaries where there is little, if any, potential for development with current ADT levels below 2000. Access connection spacing below the values shown in this table may be approved based on safety and operational considerations as determined by TxDOT.

Corner clearance refers to the separation of access connections from roadway intersections. Table 2-2 provides minimum corner clearance criteria.

Where adequate access connection spacing cannot be achieved, the permitting authority may allow for a lesser spacing when shared access is established with an abutting property. Where no other alternatives exist, construction of an access connection may be allowed along the property line farthest from the intersection. To provide reasonable access under these conditions but also provide the safest operation, consideration should be given to designing the driveway connection to allow only the right-in turning movement or only the right-in/right out turning movements if feasible.

Auxiliary Lanes

This subsection describes the basic use and functional criteria associated with auxiliary lanes. Auxiliary lanes consist of left-turn and right-turn movements, deceleration, acceleration, and their associated transitions and storage requirements. Left-turn movements may pose challenges at driveways and street intersections. They may increase conflicts, delays, and crashes and often complicate traffic signal timing. These problems are especially acute at major highway intersections where heavy left-turn movements take place, but also occur where left-turn movements enter or leave driveways serving adjacent land development. As with left-turn movements, right-turn movements pose problems at both driveways and street intersections. Right-turn movements increase conflicts, delays, and crashes, particularly where a speed differential of 10 mph or more exists between the speed of through traffic and the vehicles that are turning right.

Table 2-3 presents thresholds for auxiliary lanes. These thresholds represent examples of where left turn and right turn lanes should be considered. Refer to the TxDOT Roadway Design Manual, Chapter 3, for proper acceleration and deceleration lengths.

Anchor: #i1000848Table 2-3: Auxiliary Lane Thresholds
Median Type	Left Turn to or from Property		Right Turn to or from Property ⁽⁵⁾
	Acceleration	Deceleration	Acceleration	Deceleration
Non-Traversable (Raised Median)	(2)	All	Right turn egress > 200 vph (4)	> 45 mph where right turn volume is > 50 vph (3) where right turn volume is > 60 vph (3)
Traversable (Undivided Road)	(2)	(1)	Same as above	Same as Above
(1) Refer to Table 3-11, TxDOT Roadway Design Manual, for alternative left-turn-bay operational considerations. (2) A left-turn acceleration lane may be required if it would provide a benefit to the safety and operation of the roadway. A left-turn acceleration lane would interfere with the left-turn ingress movements to any other access connection. (3) Additional right-turn considerations: Conditions for providing an exclusive right-turn lane when the right-turn traffic volume projections are less than indicated in Table 2-3: High crash experience Heavier than normal peak flow movements on the main roadway Large volume of truck traffic Highways where sight distance is limited Conditions for NOT requiring a right-turn lane where right-turn volumes are more than indicated in Table 2-3: Dense or built-out corridor where space is limited Where queues of stopped vehicles would block the access to the right turn lane Where sufficient length of property width is not available for the appropriate design (4) The acceleration lane should not interfere with any downstream access connection. The distance from the end of the acceleration lane taper to the next unsignalized downstream access connection should be equal to or greater than the distances found in Table 2-2. Additionally, if the next access connection is signalized, the distance from the end of the acceleration lane taper to the back of the 90th percentile queue should be greater than or equal to the distances found Table 2-2. (5) Continuous right-turn lanes can provide mobility benefits both for through movements and for the turning vehicles.1 Access connections within a continuous right turn lane should meet the spacing requirements found in Table 2-2. However, when combined with crossing left in movements, a continuous right-turn lane can introduce additional operational conflicts.

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Emergency Access

Direct emergency access (to be used by authorized emergency vehicles only) may be permitted if it is not feasible to provide adequate emergency access to a secondary roadway. A written explanation with references to local criteria from an appropriate government public safety official will be included with the permit application.

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Field Driveways

Field driveways will be permitted where, in the determination of TxDOT, the field has no other reasonable access. Typically, one field driveway to a property under the same ownership or controlling interest may be granted; additional field driveways may be permitted if the necessity for such additional access (due to topography or ongoing agriculture activities) is demonstrated. Field driveways will be kept to the minimum necessary in order to provide reasonable access. A permit for a field driveway will state the conditions as to its use by agricultural equipment only. A change in the use of the property may require a reevaluation of the access permit as determined by the Department or municipality that has been granted access connection location permit authority.

1. Florida Department of Transportation (FDOT), Florida's Driveway Handbook, 2002.