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SR 904 - Cheney to Four Lakes Project - Route Development Plan - Chapter 3

Present & Projected Operating Conditions

Traffic Volumes

Traffic volumes along SR 904 vary according to the time of day, season, and whether Eastern Washington University is in session or not. Existing annual average daily traffic (AADT), PM peak hour traffic (evening commute), and turning movement volume data was collected along the mainline and at major county intersections on SR 904 for analysis in this RDP. The following tables summarize the findings:

Chart of Average Daily Traffic

 Table 10 * traffic counts not available
Source: 1999-2002 Annual Traffic Report and WSDOT TRIPS System ** Based on 2.5% growth rate from year 2002 &

2003 actual counts

K% -ratio of design hour traffic to AADT

Growth Rate

Traffic volumes were projected to 2023 for long term analysis. The 2.5% growth rate was derived from historic counts acquired from WSDOT Traffic Data Office. (See Table 10)

Level of Service

A level of service (LOS) analysis evaluates the traffic volumes and operational characteristics of a designated segment of a highway. The product of the analysis is a description of the highway’s traffic carrying capacity as defined by six levels of service. Level of Service is a qualitative measure describing operational conditions within a traffic stream, generally described in terms of such factors as speed and travel time, freedom to maneuver, traffic interruptions, comfort and convenience, and safety. The levels of  service range from LOS A representing the best operating conditions to LOS F representing the worst.

Level of Service Operating Conditions
A Free-flow operations at average travel speeds Vehicles completely unimpeded within the traffic stream Platoons of three or more vehicles are rare
B Reasonably unimpeded operations at average travel speeds Maneuverability within traffic stream is slightly restricted Drivers delayed in platoons up to 50% of the time
C (minimum LOS for Rural highways in Washington) Stable operations Ability to maneuver becomes more restrictive Drivers delayed in platoons up to 65% of the time
D (minimum LOS for Urban highways in Washington) Unstable traffic flow Small increases in flow may cause substantial increases in delays and speed Passing demand high but passing capacity approaches zero Drivers are delayed in platoons for nearly 80% of the time
E Significant delays and average travel speeds less than base condition Adverse progression, passing is virtually impossible
F Heavily congested flow with traffic demand exceeding capacity High delays and queuing expected

Table 11

Source: Highway Capacity Manual 2000

Level of service analysis for this RDP was accomplished using the Special Report Highway Capacity Manual (HCM) methodology for two-lane highways. All of the intersections within the RDP limits are unsignalized. WSDOT Eastern Region Planning and Traffic offices have drafted a Signal and Channelization Priority Array that identifies and ranks intersections recommended for signalization. The intersection of SR 904 and Medical Lake Four Lakes Road was analyzed in the Signal and Channelization Priority Array. Out of 21 potential signal locations currently under consideration this intersection ranked 5th which met all criteria.

To provide detailed intersection operational analysis at significant intersections within the RDP limits, turn movement counts were collected. While the LOS at unsignalized intersections is measured in terms of average vehicle delay, the overall intersection LOS is based on the LOS of the worst approach movement. Projected traffic counts that were based on an average growth rate of 2.5% were used to analyze the LOS for each approach. The LOS was calculated using existing PM peak hour volumes. The table below shows the results of the analysis.

Two Way Stop Control Intersections

Intersection 2003 2023 (No Build)
Minor Rd. EB Minor Rd. WB SR 904 NB SR 904 SB Minor Rd. EB Minor Rd. WB SR 904 NB SR 904 SB
Medical Lake/Four Lakes Rd. D A A F A A
Old PSH 11 C A A E A A
Meadow Lake Rd. C A A C A A
Jensen Rd. D D A A F F A A

Table 12

With the projected traffic volumes in year 2023 for the 5 lane facility, Medical Lake/Four Lakes intersection will operate at LOS A with a signal. The remaining three intersections: Old PSH 11, Meadow Lake, and Jensen will also operate at LOS A on mainline. The minor streets of Meadow Lake and Old PSH 11 will operate at LOS C & D respectively, while Jensen will operate at LOS E. A traffic signal may be proposed at this intersection if at the time of design it meets signal warrants.

Analysis of control delay, queue length, and v/c ratio at each intersection for year 2003 indicates that Medical Lake/Four Lakes Rd intersection has a high queue length. Control delays are used to analyze the effects of coordination, actuation, and congestion. The 95th percentile queue length represents a reasonable worst case scenario. WSDOT designs turn lanes with sufficient storage lengths to accommodate the 95th percentile queue when possible. Volume to Capacity Ratio (v/c) indicates the amount of congestion. Any ratio greater than or equal to 1 indicates that the approach is operating at above capacity. See table 13 below


Intersection Control Delay(sec) 95% Queue Length(ft) Max. v/c Ratio
Medical Lake/Four Lakes Rd. 28.4 56 0.46
OLD PSH 11 19.6 1 0.41
Meadow Lake Rd. 21.3 1 0.32
Jensen Rd. 29.2 2 0.03

Table 13


WSDOT uses two major programs, the High Accident Location (HAL) and the High Accident Corridor (HAC) programs, to address areas with frequent collisions along state highways.

Threshold criteria for identifying HAL and HAC locations include total points per mile(based on

point values assigned to severity of accidents), number of accidents per mile, and average

severity per mile. Severity point assignment are shown below.

10 points per fatal accident
9 points per disabling injury accident
3 points per evident injury accident
2 points per possible injury accident
1 point per property damage only accident

Currently, there have not been any HAL’s or HAC’s identified on this segment of SR 904. However, given the recent increase in fatalities in this area, MP 11.50 to MP 13.49 and MP 14.00 to MP 14.99 along this segment of SR 904 is designated a HAC in the 05-07 biennium. Severity points were calculated for the last three years and showed a significant decrease in the points (see table below).

Year Severity Points
1999 79


2001* 37

*Data through November 30, 2001


The State’s Transportation Data Office is supplied with the reported traffic accidents from the Washington State Patrol (WSP) that are $500 or more. This data is compiled and a

report is created called “Washington State Highway Accident Report”. Accident and fatality rates on a segment of highway are typically compared to statewide rates as well as rates for the region, state functional classification and county based on single or multi-year periods. The table below shows these comparisons. Due to delays in implementing a new collision records system in the state, the most recent year covered by this report (for comparing statewide data) is 1996. The 1999 – 2000 Collision Data Summary will be available soon.

Chart of Accident Data

Source:  Run Date: 6/16/2000 (Includes partial accident records)

*Accident Rate = (Number of Accidents) x ( 1million) (Section Length**) x (AADT) x (365 Days)

In 1996, the accident rate for Spokane County was 2.16 accidents per million vehicle miles of travel compared to the statewide and eastern region average accident rates of 1.88 and 1.82, respectively. During this same period the average accident rate along minor arterials in rural areas was 1.82. Accident data from November 30,1998 to November 30, 2001 for SR 904 between MP 12.51 and MP 16.74 reveals the following:


Table 15

Source: Trips data
(Above data contains both full and partial accident records.)


Injury Type Number of Collisions % Total
Property Damage Only 21 35
ALL Injury 37 62
Possible Injury 15 25
Evident Injury 18 30
Disabling Injury 4 7
Fatal 1 1.5
Injury Status Unknown 1 1.5
Total Accidents 60 100
Non-Collision (fire) 2 N/A
Non-Domestic Animal PDO 4 N/A

Table 16

Source: Trips Data
(Above data contains both full and partial accident records.)

Charts of Collisions