HomeMy WebLinkAboutA005 - memo dated January 5, 1996 from Traffic Engineer to Planner on traffic impact study M E M O PUBLIC WORKS DEPARTMENT
CITY OF AMES
TO: Eden Schmitt, Planner
FROM: Scott Logan, City Traffic Engineer
DATE: January 5, 1996
SUBJECT: Traffic Impact Study for the Suncrest Development
I was contacted by the developer, Jensen Homes about conducting a traffic impact study
for the Suncrest Development. According to Mike Despeard, concerns have been raised
by residents in the Green Hills Subdivision about the traffic impact on Oakwood Road.
These residents were concerned that additional conflicts would be caused due to the
additional traffic generated from the subdivision. Residents also are concerned about the
45 mile per hour speed limit that exists on Oakwood Road. As indicated previously to
residents, this speed limit will be lowered when traffic conditions change on this street.
Currently, studies have showed that the vast majority of the drivers are travelling at speeds
greater than 40 miles per hour. With additional development, staff believes that speeds w0l
be lowered due to the changing traffic conditions.
The developer had requested that staff perform the traffic impact study for the
development. I have committed to performing a cursory impact study that would generally
review conditions resulting from the additional traffic generated by the development.
However, the developer will be responsible for any additional study if the need arises. It
has been the City's policy for developers to perform their own traffic study if concerns are
raised about traffic problems.
According to the developer, the subdivions will contain 75 single family lots and will have
a primary access onto Oakwood Road at White Oak Drive. According to the Institute of
Transportation's "Trip Generation" Manual, the traffic generated from this fully developed
subdivision will be approximately 750 vehicles per day. This is a generation of 10
vehicular trips per day for each single family residence. It should be noted that this trip
generation closely resembles the actual trip generation from single family developments
in Ames. Attached is the trip generation guide that shows the number of vehicular trips for
single family residential units.
Staff believes that the traffic volumes will primarily be egressing and ingressing the
subdivision from White Hill Drive. Also, it is believed that the traffic would primarily travel
from White Hills Drive on Oakwood Drive to the Elwood Drive intersection. With this
distribution, traffic along this section of Oakwood Drive would increase by 750 vehicles per
day (vpd), from 1680 vpd to 2430 vpd. This additional traffic would not detrimentaN
impact conditions on Oakwood Drive since the capacity threshold for this two-lane facilitv
is 9,000 vehicles per day. As discussed in studies performed for both the Hyland widening
and the 24th Street parking prohibitions, the two-lane traffic facility would be widened to
three or four lanes when volumes exceed this 9,000 vpd threshold . Currently the projected
traffic volume for Oakwood Road would be significantly below this threshold.
Also, the additional traffic generated by the subdivision would create delay problems at the
Elwood/Oakwood/Airport Road intersection. Currently, the intersection is controlled by a
four-way stop, stopping vehicles on all approaches. This intersection is currently operating
at a level of service A condition with minimal delays. It is not expected that this condition
would change with the projected traffic volumes generated by the new development.
Traffic would have to increase by two to three fold on all approaches before the conditions
would fall below a LOS C. Incidently, the City has adopted a LOS C factor as the
threshold service factor, whereby improvements would be considered when conditions fall
below this level.
Staff does believe that with the development, pedestrian crossing signage should be
erected on Oakwood Road at the White Oak Drive intersection. It is realized that
pedestrians from the new subdivision would cross Oakwood Road to walk in the residential
area to the south. Due to the projected traffic volumes at the intersection, traffic warrants
would not be met for establishing either a four-way stop control, or traffic signals at this
intersection.
Single-Family Detached Housing
(210)
Average Vehicle Trip Ends vs: Dwelling Units
On a: Weekday
Number of Studies: 348
Average Number of Dwelling Units: 206
Directional Distribution: 50% entering, 50% exiting
Trip Generation per Dwelling Unit
Average Rate Range of Rates Standard Deviation
9.55 4.31 - 21 .85 3.66
Data Plot and Equation
30,000
N
C
W 20,000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X
a
U X
X
N
X
ro
m :
Q10,000 - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - - - - - . . . . . ... . - - - - - . . . .
Ix
11 X
X : X
' X
0
0 1000 2000 3000
X = Number of Dwelling Units
X Actual Data Points Fitted Curve ------ Average Rate
Fitted Curve Equation: Ln(T) = 0.921 Ln(X) + 2.698 R2 = 0.96
tqP Generation, January 1991 257 Institute of Transportation Engineers