Consistency and Design Speed

HIGHWAY RAILROAD
ENGINEERING
Group 2
Madrio, Thomas Jason
Monterola, Vincent Bryan
Monungolh, Meil Justin
INSTRUCTOR: ENGR. ROXANNE C. GALDO, ME-1, M.ENG

CONSITENCY AND
DESIGN SPEED
CONSISTENCY
• Is The Most Important Single Rule in • Measures of vehicle operations
Highway Design • Speed variance
• Lateral placement
• Should not violate driver expectations (mean and variance)
• Erratic maneuvers
• Guidance level errors • Traffic conflicts
• SPEED-PROFILE MODEL • Driver Workload

DESIGN AND SPEED
• LOCAL ROADS AND STREETS
• LOCAL RURAL ROADS
• LOCAL URBAN ROADS
• COLLECTOR ROADS AND STREETS
• RURAL COLLECTORS
• URBAN COLLECTORS
• RURAL AND URBAN ARTERIALS
• RURAL ARTERIALS
• URBAN ARTERIALS
LOCAL RURAL STREETS: DESIGN SPEED
LOCAL URBAN STREETS: DESIGN SPEED
• For consistency in design elements, design speeds ranging from 30 to 50 km/h [20 to 30 mph] may be
used, depending on available right-of-way, terrain, likely pedestrian presence, adjacent development,
and other area controls.
• In the typical street grid, the closely spaced intersections usually limit vehicular speeds, making the
effect of design speed less important.
• Since the function of local streets is to provide access to adjacent property, all design elements should
be consistent with the character of activity on and adjacent to the street, and should encourage speeds
generally not exceeding 50 km/h [30 mph].

RURAL COLLECTORS: DESIGN SPEED
• Low design speeds of 70 km/h [45 mph] and below are generally applicable to highways with curvilinear
alignment in rolling or mountainous terrain, or where environmental Collector Roads and Streets (Rural)
425 conditions dictate.
• High design speeds of 80 km/h [50 mph] and above are generally applicable to highways in level terrain
or where other environmental conditions are favorable.
• Exhibit 6-1 identifies minimum design speeds for rural collector roads as a function of the type of terrain
and design traffic volumes.
• The designer should strive for higher values than those shown where specific safety concerns are
present and costs are not prohibitive.

URBAN COLLECTORS: DESIGN SPEED
• For consistency in design, a design speed of 50 km/h [30 mph] or higher should be used for
urban collector streets, depending on available right-of-way, terrain, adjacent development,
likely pedestrian presence, and other site controls.
• See Exhibit 6-1 and the section on “Design Speed” in Chapter 2 for additional information.
• In the typical urban street grid, closely spaced intersections often limit vehicular speeds
and thus make the consideration of design speed of lesser significance.
• Nevertheless, the longer sight distances and curve radii commensurate with higher design
speeds result in safer highways and should be used to the extent practical.
RURAL ARTERIALS: DESIGN SPEED
75 mph] depending on terrain, driver expectancy and, in the case of reconstruction projects, the
alignment of the existing facility.
Design speeds in the higher range — 100 to 120 km/h [60 to 75 mph] — are normally used in
level terrain
esign speeds in the midrange — 80 to 100 km/h [50 to 60 mph] — are normally used in rolling
terrain.
esign speeds in the lower range — 60 to 80 km/h [40 to 50 mph] — are used in mountaino
terrain. Where a lower design speed is used.

URBAN ARTERIALS: DESIGN SPEED
• Design speeds for urban arterials generally range from 50 to 100 km/h
[30 to 60 mph].
• Lower speeds apply in central business districts and in more developed

areas
• Higher speeds are more applicable to outlying suburban and

developing areas.
CROSS-SECTION OF THE
TYPICAL HIGHWAY
•
•
• For Collector Roadway, 6.00 meters wide surface is acceptable only for low
volume traffic including few trucks traveling thereon.
• For Local Rural Roadway, the minimum surface width is 4.80 meters for a
30 km / hr. design speed.
• For Urbair Roadway, the minimum design width is 3.60 meters although 3.00
meters is allowed where space is limited.
Where there are heavy meetings or overtaking between cars and trucks, air
disturbances sometimes cause side collision between passing vehicles when
swerved within or out of their lanes. Motorists are requesting for wider lanes.
CROSS-SECTION OF A ROAD
A. Roadway
B. Surface Course
C. Pavement Marking, white solid line
D. Base
E. Bed
F. Base Course
G. Sub-base
H. Subgrade
I. Embankment
J. Earth Foundation
K. Pavement Marking, white broken
line
CROSS-SECTION OF TYPICAL HIGHWAY
ROAD SHOULDER
Road shoulder or verge is defined as that portion of the roadway
between the edge of the traffic lane and the edge of the ditch,
gutter, curb or side slope. AASHTO requires that its usable
pavement width shall be strong enough to support vehicles.
ROAD SHOULDER
IMPORTANCE OF ROAD SHOULDER
1. Road shoulder serves as a place for vehicles to stop when disabled or
for some other purposes. Road shoulder considerably reduces road
accidents.
2. The road capacity is decreased and accident opporrunity increases if

the shoulder is too narrow or omitted in the design.
3. Shoulder should be continuous along the full length of the roadway.

It also adds structural strength to the road pavement.
4. Shouldler increases the horizontal sight distance on curves. It

reduces accident potential when vehicle stop during emergencies.
Most of the road shoulders in rural areas are unpaved having a width of
60 to 120 centimeters wide either earth filled or graveled surface that
during rainy days, drivers are hesitant to occupy. The Uniform Traffic
Control Device Manual provides that:
"All inter-town or city highways shall be provided with edge line and
may be used on other classes of roads."
A continuous narrow white line strip at the edge of the roadway that
separates the shoulder, serves as guide to drivers during bad weather
and poor visibility conditions. The white strips tend the driver to stay in
the traffic lane and the vehicles seldom infringe on the shoulder.
POLICY OF GEOMETRIC DESIGN
• Outside shoulder should be paved for at least 3.00 or 3.60 meters wide
if truck volume is more than 250 in the design hour (ADT).
• The recommended width of left (median) shoulder is 1.20 to 2.40 meters with at last 1.20 meters paved.
• If there are 6 or more lanes, the median shoulder should be 3.00 meters wide or 3.60 meters if truck volume in the design hour exceeds 250.
• For arterials with ADT less than 400 the usable shoulder width is fixed at 1.20 meters minimum, although 2.40 meters wide is much preferred.
• When the design hour volume ADT exceeds 400, the usable minimum shoulder width is 2.40 meters although 3.60 meters is recommended.
6. For Urban Arterial Road, similar shoulder without curb is suggested
unless needed for proposed drainage.
7 . The width of median shoulder on four lanes divided arterials is fixed
at 90 centimeters as minimum.
8. For six or more lanes, 2.40 to 3.00 meters shoulder width is
recommended.
9. For Rural Collectors Roadway, 60 centimeters wide graded shoulder is
required for ADT's less than 400"
10. For ADT's over 2000. 2.40 meters wide shoulder is recommended.
Considering the above recommendations, Width is defined as
"extending from the edge of the surfacing to the point where
shoulder slope intersect the side slope. " The Urban colleclor
road usually has no shoulder, instead, parking lanes of 2.40
meters or preferably 3.00 meters wide with gutters are specified.
END

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HIGHWAY RAILROAD

INSTRUCTOR: ENGR. ROXANNE C. GALDO, ME-1, M.ENG

• SPEED-PROFILE MODEL • Driver Workload

• LOCAL URBAN ROADS

• COLLECTOR ROADS AND STREETS

• RURAL AND URBAN ARTERIALS

and other area controls.

effect of design speed less important.

generally not exceeding 50 km/h [30 mph].

425 conditions dictate.

or where other environmental conditions are favorable.

and design traffic volumes.

present and costs are not prohibitive.

urban collector streets, depending on available right-of-way, terrain, adjacent development,

likely pedestrian presence, and other site controls.

and thus make the consideration of design speed of lesser significance.

alignment of the existing facility.

terrain. Where a lower design speed is used.

• Lower speeds apply in central business districts and in more developed

• Higher speeds are more applicable to outlying suburban and

volume traffic including few trucks traveling thereon.

30 km / hr. design speed.

meters is allowed where space is limited.

disturbances sometimes cause side collision between passing vehicles when

C. Pavement Marking, white solid line

K. Pavement Marking, white broken

2. The road capacity is decreased and accident opporrunity increases if

3. Shoulder should be continuous along the full length of the roadway.

4. Shouldler increases the horizontal sight distance on curves. It

7 . The width of median shoulder on four lanes divided arterials is fixed

8. For six or more lanes, 2.40 to 3.00 meters shoulder width is

9. For Rural Collectors Roadway, 60 centimeters wide graded shoulder is

required for ADT's less than 400"

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