§ 3.4.14. Traffic Delay Data

All of these data are used to estimate the traffic delay costs associated with the construction of a future overlay within a given design strategy. Unless heavy traffic and/or large delays are expected, these costs are not normally significant.

A.

Detour Model Number

Five different types of traffic detour models can be used to route traffic through the restricted overlay zone. These models are illustrated in Figure 3-10 and 3-11 in Appendix H of this manual. Note: In cases where the future average daily traffic approaches or exceeds the capacity of the facility (approximately 1,500 vehicles per hour per lane) during overlay construction, it is possible that the Municipal Flexible Pavement Design - 1 program may generate unusually low or even negative user delay costs. In these cases, it is recommended that the Detour Model 5 as indicated in Figure 3-11 in Appendix H of this manual be used to recognize that most vehicles in the traffic stream would seek an alternate route around the construction zone.

B.

Number of Open Lanes Through Restricted Overlay Zone

There are two input variables associated with this; one for the overlay direction and one for the nonoverlay direction. Obviously, both depend on the detour model selected.

C.

Average Approach Speed to Overlay Zone

In order to determine how long a vehicle is delayed due to overlay construction, it is necessary to define how fast it could be traveling if it were not affected. Approach speed indicates normal travel speed.

D.

Average Speed Through Restricted Zone

The two variables associated with this (speeds in overlay and nonoverlay direction) are both used along with the average approach speed to predict the lost time to vehicles in each direction due to interference that occurs during overlay construction.

E.

Distance Traffic Is Slowed

The two variables associated with this (distances in overlay and nonoverlay direction) are also used in conjunction with the latter three vehicle speeds to estimate total user time delay.

F.

Detour Distance Around Overlay Zone

This variable applies only to Detour Model 5. It identifies the length of the detour route over (other city streets) which traffic would be detoured or traffic would seek out.

G.

Number of Hours Per Day Overlay Construction Occurs

This variable is used to determine how many days of delay will be required to complete overlay construction.

H.

Average Daily Traffic Arriving Each Hour of Construction (Municipal Flexible Pavement Design - I Only)

This variable is used to determine how many vehicles will be delayed for each day of construction. The percentage should be indicative of the average percentage of the daily traffic that will arrive during construction.

I.

Beginning and Ending Times of Overlay Construction (Municipal Rigid Pavement Design Only)

The Municipal Rigid Pavement Design has a built-in distribution of daily traffic for urban areas in Texas. Thus, if the beginning and ending times of overlay construction for a given day are provided, the program will determine the total number of vehicles that will be delayed.

TABLE 3-9 RECOMMENDED SALVAGE VALUES
MUNICIPAL RIGID PAVEMENT DESIGN VALUES
Subgrade PI Range	Percent
	Subbase	Concrete	HMAC Overlays
0-20	20	30	30
25-50	10	30	30
MUNICIPAL FLEXIBLE PAVEMENT DESIGN VALUES
		Percent
HMAC		30
Flex Base		20
Lime Subbase		20
Overlay		30
Source: ARE, Inc.

 

TABLE 3-10 PAVEMENT DESIGN COEFFICIENT TABLE
SDHPT Stiffness Coefficients	Description	Suggested AASHTO Layer Coefficients
0.32	Lime Treated Subgrade	0.11
	Cement Treated Subgrade	0.23
0.5	Flexible Base	0.14
	RCP (New)	0.5
	RCP (Old in Fair Cond.)	0.4
	RCP (Old Pumping)	0.1
	RCP (Old Pumping to be under sealed)	0.35
0.96	HMAC Type C	0.4
0.96	HMAC Type D	0.44
0.9	Asphalt Stabilized Base	0.3
Source: City of Austin, Department of Public Works and Transportation

 

Table 3-11 Summary of Minimum Paving Thickness
Street Classification	ROW Width (Ft.)	Paving Width E-E (Ft.)	Width of Median F-F (Ft.)	Initial ADT (VPD)	Percent Growth (%)	Total Equivalent 18K Single Axle Load Applications (20 Year Flexible Design)	Min. Thickness of HMAC Surface Course (In.)	Min. Thickness of Flexible Base Course (In.)**
Local
SF-1 to SF-2	50	27		500	3	20,000	1½	8
SF-3 to SF-6	56	33		500	3	20,000	1½	8
Collectors
Residential	60	37		1,000	3.5	80,000	2	10
Neighborhood		41		2,000	4	290,000	2	10
Commercial	70	45		5,000	4	1,240,000	3½	12
Industrial	90	57		2,000	4	930,000	3	12
Prim, Undiv, 4	70	45		3,500	4	650,000	2½	12
Prim, Undiv, 5	90	57		3,500	4	850,000	3	12
Prim, Undiv, 4-LN	90	2 @21	16	6,000	4	1,020,000	3½	12
Prim, Undiv, 6-1-N	120	2 @33	23	8,000	4	2,010,000	3½	12
Arterials
Minor, Undiv.	70	48		6,000	4	1,020,000	4	12
Minor, Undiv, 5	90	60		8,000	4	2,680,000	4	12
Minor, Div, 4-LN	90	2 @24	16	9,000	4	3,020,000	4	12
Major, Div, 6-LN	120	2 @36	23	18,000	4	5,200,000	5	12
Major, Div, 8-LN	150	2 @48	23	25,000	4	6,300,000	5	12
History of this Section: Subdivision Information Memorandum E-74-7, E-76-4, E-76-14, E-76-18 and E-78-3.
Min. pavement thickness originally contained in Subdivision Memorandum E-76-14 and E-76-18 and alternate thickness rock subgrade are restated above without revision.
These values are minimums and are not to be used without verification by a computerized pavement design for specific site subgrade and local traffic conditions.