Design For Accessibility: Getting it right from the start
Design-Criteria-for-Highway-and-Railways.pptx
1. Design Criteria for Highway and
Railways
Group 2 Members: Allen Justine Burce Harly Dave Dagohoy
Jayson Casaljay Victhur Morillo
2. Design Criteria for
Highway and Railways
Consistency
Consistency is the most important single rule in highway
design. That is, by making every element of the roadway conforms
to the expectation of every driver.
Drivers expect the highway agency to provide them with:
1. Clear information and guidance through a variety of road signs.
2. Avoiding abrupt changes in the traffic as well as the road
standards.
3. Design Criteria for
Highway and Railways
If these guides and directions could be planned properly to
convey one single message at a time, and if these directions will be
followed smoothly and easily without undue haste, or changes in
speed, then, the roadway facilities are considered satisfactory.
Experienced highway Engineers recommended that highway signs
and directions should be integrated as early as the preliminary
layout studies.
4. Design Criteria for
Highway and Railways
The Design Speed
There is no single set of Geometric Standards that will
apply to all highways. For every highway segment, decisions
regarding appropriate control for each of the many details or
requirements must be addressed individually or separately.
Basic Design Features refers to the tightness and super
elevation of curves, the sight distance, and grade. The design
speed is basically higher than the anticipated average speed.
5. Design Criteria for
Highway and Railways
For economic reasons, the Geometric Features of certain
road sections are designed for speed from 30 to 50 kilometers per
hour. And yet, some motorists drive faster on straight road
alignment or less sharply curved sections. Under these situations,
highway design adopted control by reducing the super elevation
combined with easement curves, delineators, stripping signs and
rumble strips, to alert motorists and inform them that they are
approaching sharp curves or blind curves.
7. Design Criteria for
Highway and Railways
The AASHTO practice is to classify first the highway as Rural
or Urban, then as Freeways, Arterials, Collectors and Local. Rural
collectors and local facilities are classified as flat, rolling, or
mountainous. Although the design speed presently used is 80 km.
per hour, highway designers projected design speed up ta 120
kilometers per hour to guarantee against future obsolescence as
well as the increased margin of operating safety. The high speed
road design must anticipate future generation high speed vehicles
and advanced transportation systems that may operate on many
of these road alignments.
8. Design Criteria for
Highway and Railways
Although the design speed of most highways is governed
by construction costs, the concept of the relatively high speed
design for freeways is Regardless of Cost. They are planned for a
nationwide high volume traffic and high speed network.
10. Design Criteria for
Highway and Railways
AADT or ADT refers to traffic volume or flow on a highway
as measured by the number of vehicles passing a partial station
during a given interval of time. It is called "Average Annual Daily
Traffic". if the period is less than one year. Volume may be stated
on hourly "Observed Traffic Volume" or estimated 30th hour
volume commonly used for design purposes. Some highway
agencies use traffic volume for 5 minutes interval to distinguish
short peak movements of vehicles.
11. Design Criteria for
Highway and Railways
Speed Implications
Research shows that lower speeds lead to fewer and less
serious crashes. There are two reasons for this:
• At higher speeds a rider or a driver has less time to react to a
situation and therefore there is a greater likelihood that an
error will result in a crash; and
• The momentum and kinetic energy of a vehicle increases
rapidly with speed. The sudden dissipation of this energy in a
crash means that the injury to occupants is more severe.
Therefore, a carefully planned speed limit regime can make a
significant contribution to road safety.
12. Design Criteria for
Highway and Railways
Current Speed Limits
The current speed restrictions are set out in Chapter IV –
Traffic Rules, in Republic Act No. 4136 Land Transportation and
Traffic Code.
The rules indicate that a motorist shall drive at a safe speed
determined by the driver based on the road environment
conditions. There are however maximum allowable speeds for
different road environments.
13. Design Criteria for
Highway and Railways
On open country roads with no "blind corners" not closely
bordered by habitation, the maximum speed for passenger cars
and motorcycles is 80 kph and for motor trucks and buses, 50 kph.
On "through streets" or boulevards clear of traffic, with no
"blind corners", when so designated, the maximum speed for
passenger cars and motorcycles is 40 kph and for motor trucks and
buses, 30 kph.
14. Design Criteria for
Highway and Railways
On city and municipal streets, with light traffic, when not
designated "through streets," the maximum speed for passenger
cars, motorcycles, motor trucks and buses is 30 kph.
Where it is determined that a road should have a different
speed restriction to that indicated above, then specific speed
restriction signs should be installed to inform motorists. The
following sections describe where certain speed restriction could
be appropriate.
15. Design Criteria for
Highway and Railways
High Risk Pedestrian Areas – 40 kph
Vulnerable road users, especially pedestrians, are
particularly vulnerable at higher speeds. The graph below based
on international research shows the risk of a pedestrian fatality if
hit by a vehicle at different speeds.
17. Design Criteria for
Highway and Railways
For instance, 25% of people struck by a vehicle traveling at
40 kph would suffer fatal injuries. At 50 kph this risk increases to
85%. Therefore, a speed limit of 40 kph or lower would be
appropriate on roads where there is high pedestrian activity such
as in city areas.
A 40 kph speed limit would also be appropriate on roads
where there are no one footpaths and pedestrians are required to
walk on the road.
18. Design Criteria for
Highway and Railways
Low risk pedestrian areas – 60 kph
On roads through built-up areas where there are not so
many pedestrians. It is appropriate to allow motorized traffic to
travel more quickly.
The following pictures shows the type of environment
where 60 kph may be appropriate. Although this road is carrying
vulnerable road users, they have separate lane to travel in.
20. Design Criteria for
Highway and Railways
80 kph
An 80 kph speed limit would be appropriate on a high
standard duplicated carriage road where there is only occasional
access from adjoining properties.
100 kph
A 100 kph speed limit would only be appropriate on very
high standard expressways, which have a low crash rate. These
expressways should have a high standard geometry and should be
free of roadside hazards. If
21. Design Criteria for
Highway and Railways
Speed Restriction Signs
Good speed management practice depends on speed limit signs
being placed in visible locations and repeated frequently enough for
motorists to be certain of which speed zone they are in.
At the start of a new speed zone, a speed limit sign should be
erected on the left and right sides of the road. Then within the first
kilometer, there should be two (2) farther pairs of repeater speed limit
signs.
After that, repeater signs should be placed at one kilometer
spacing. Repeater signs should also be placed before and after all major
intersections to confirm the speed limit to all traffic turning into the road
being considered.
22. Design Criteria for
Highway and Railways
Poor Road Standards
If the standard of the road geometry or its surface is poor, then it
may be appropriate to adopt a lower speed limit than would normally
apply until such time that the road improvements can be made. The
lower speeds compensate for the hazardous conditions of the road.
An 80 kph or 90 kph speed limit may also be appropriate on
lower standard expressways. For instance, the concrete plant cylinders
on the side of the expressway as shown below are a serious road hazard
within the clear zone which would cause injury to the occupants of an
out of control vehicle. If this road hazard cannot be removed or
protection for vehicles provided, the speed limit should be restricted to
reduce the risk to motorists and riders.
24. Design Criteria for
Highway and Railways
Road Capacity
Road capacity, as defined in the U.S. Highway Capacity
Manual (HCM), is the maximum number of vehicles, which have a
reasonable expectation of passing over a given section of a lane or
a roadway in one direction or in both directions during one hour
under prevailing road and traffic conditions.
Generally, road capacity with respect to road sections is
measured in terms of level-of-service. This is designated with
letters ‘A’ and ‘F’ with ‘A’ the most ideal condition and ‘F’ the
saturated condition where volume is equal to the road capacity.
25. Design Criteria for
Highway and Railways
In regard to intersections, capacity is generally measured in terms of
‘degree of saturation’
The capacity of a route can be affected by the following factors:
• Number of Lanes;
• Lane and shoulder width;
• Terrain and road gradient;
• Traffic composition;
• Side friction such as the presence of road furniture and pedestrians;
and
• Intersection capacity (priority and movements, traffic signal phasing,
number of lanes, etc.)
26. Design Criteria for
Highway and Railways
Ideal capacity of a road is 2.000 vehicles/hour (vph).
However, based on several surveys conducted in Metro Manila for
various infrastructure projects, it was found that the maximum
volume is achieve only at a level of 1,400 vph on expressways and
1,100 for urban arterials.
In the design stage of a road project, appropriate capacity
should be established to ensure satisfactory operation. In
establishing the capacity of the road, actual traffic surveys as well
as investigation of future use is required to ensure that safety is
not compromised once the facility is in operation.
27. Design Criteria for
Highway and Railways
Road Types
The basic functional types of roads are locals, collectors,
arterials and freeways. Two major considerations in the
classification of highway functional types are access to land use
and mobility. On the two extremes, the design of local streets
emphasizes access with little consideration for mobility, while the
design of freeways emphasizes mobility with limited access. The
design of collectors and arterials falls in between, with collectors
emphasizes more for access and arterials favors mobility.
28. Design Criteria for
Highway and Railways
Design Vehicles
There are generally four classes of design vehicles:
(1) passenger cars,
(2) buses,
(3) trucks, and
(4) recreational vehicles.
The passenger car category includes sport utility vehicles,
minivans, vans, and pickup trucks.
The bus and truck categories include buses and trucks of all
sizes, respectively.
29. Design Criteria for
Highway and Railways
The highway designer should exercise his judgment in
selecting the appropriate design vehicle for design control, based
on the intended use of the facility. For example, the design vehicle
from the passenger car category is adequate for the design of
parking lots and their access roads. On the other hand, a city
transit bus should be used for the design of a street in the city
along bus route, with little or no truck traffic.
30. Design Criteria for
Highway and Railways
Turning radius limits the design of horizontal curves.
Important vehicle characteristics that affect the minimum turning
radius are: minimum center line turning radius, wheelbase, track
width, and out-of-track width. AASHTO has provided the templates
for turning paths of 17 design vehicles traveling at 15 km/h. The
minimum design turning, center line turning and minimum inside
radius are listed below.
31. Design Criteria for
Highway and Railways
Driver Characteristics
Geometric design of a highway should consider users,
especially drivers’ performance limits. There are limits to a driver’s
vision, perception, reaction, concentration, and comfort that could
impact the highway safety and operating efficiency.
When driving, most drivers receive information visually
from their views of the roadway alignment, markings and signs.
They do receive other information through vehicle feedback from
the suspension system and steering control, and roadway noise.
32. Design Criteria for
Highway and Railways
The information received by a driver needs time to be processed
before a response action takes place. A well-known study on the brake-reaction
time has been made by Johannson and Rumar (1971). They reported that when
an event is expected, the driver’s reaction time has an average value of 0.6 sec.
For an unexpected event, the average reaction time is 0.8 sec. The average
brake-reaction time of a driver (including decision time), is 2.5 sec. This is
dependent on the driver’s alertness. Brake-reaction time is important in
determining sight distance in highway geometric design. Koppa (2000) has
summarized the results obtained from recent studies on brake-reaction time.
These findings are consistent with those obtained by Johansson and Rumar.
Readers may refer to Koppa (2000) for more details. Driver expectancies are
built up over time, with consistent road design. Unusual or unexpected
geometric design or event always leads to longer reaction and response time.
The geometric design of highway should be in accordance with the driver’s
expectation.
33. Design Criteria for
Highway and Railways
In recent years, there has been increased concern for older
drivers. The percentage of older drivers among the driving
population has increased over the years. Older drivers tend to
have longer reaction time, and this should be reflected in the
design.
34. Design Criteria for
Highway and Railways
Number of Lanes
The number of lanes in a segment of the highway is
determined from the estimated traffic volume for the design year
(AADT) and highway lane capacity at expected level of service.
AASHTO policies accept a dually divided 16 lanes roadway with
four lanes in each direction for an inner freeway and four more
lanes in each direction on the outside. There are some instances
where a reversible lane is located at the center of freeways with
unbalanced heavy traffic flow.
35. Design Criteria for
Highway and Railways
Level of Service Consideration
Given a fixed volume of traffic flow and vehicle composition, the
geometric design of highways, such as the horizontal and vertical curves,
grades, lane width, number of lanes, etc., affects the travel speed of
vehicles and the interaction between vehicles. The outcome of such
effect is the observable operational performance of the highway,
qualitatively represented by the highway level of service. The concept of
LOS and methods of evaluation for different highway types are covered
in great detail in the Highway Capacity Manual (TRB 2000).
The highway designer should strive to provide a LOS that is as
high as possible. AASHTO (2001) has published a list of acceptable LOS
for different road types.
36. Design Criteria for
Highway and Railways
It is recommended that, after the designer has come out
with the geometric elements of the highway (horizontal and
vertical curves, grades, super-elevation, etc.) after checking
through all the design elements, he should estimate the LOS based
on the road type, designed volume, vehicle composition, number
of lanes, and lane width. The geometric design should be revised if
the LOS is not meeting.
the expectation (for examples, by modifying the grades,
radius of curvature). He should also ensure that continuous
segments of the same highway do not have sudden change in LOS
that may cause surprise to the drivers.
38. Design Criteria for
Highway and Railways
Railroad - Highway Separation
The main question asked on a railroad and highway
separation is: 'Where one is to go over- the railroad or the
highway? If the highway is to go over the railroad, the structure
itself is lighter and the highway load is much smaller than the
railroad loads. With regards to the vertical clearance height, the
railroad requires a minimum of 7.00 meters as against 4.80 meters
clear distance above the highway. If the highway goes under the
railroad, special provision is required for the removal of rainwater
that falls within the opposing area. If the ground water is high in
the vicinity of the crossing, the roadway must be sealed against
leakage and be made heavy enough to prevent from floating.
39. Design Criteria for
Railways
DESIGN CRITERIA FOR RAILWAYS
Equilibrium speed
• When the speed of a vehicle negotiating a curved track is such
that the resultant force of the weight of the vehicle and of
radial acceleration is perpendicular to the plane of the rails, the
vehicle is not subjected to any unbalanced radial acceleration
and is said to be in equilibrium.
• This particular speed is called the equilibrium speed. The
equilibrium speed, as such, is the speed at which the effect of
the centrifugal force is completely balanced by the cant
provided.
40. Design Criteria for
Railways
Maximum permissible speed
• This is the highest speed permitted to a train on a curve taking
into consideration the radius of curvature, actual cant, cant
deficiency, cant excess, and the length of transition.
• On curves where the maximum permissible speed is less than
the maximum sectional speed of the section of the line,
permanent speed restriction becomes necessary
41. Design Criteria for
Railways
Cant deficiency
• Cant deficiency (Cd) occurs when a train travels around a curve
at a speed higher than the equilibrium speed. It is the
difference between the theoretical cant required for such high
speeds and the actual cant provided.
42. Design Criteria for
Railways
Cant Excess
• Cant excess (Ce) occurs when a train travels around a curve at a
speed lower than the equilibrium speed. It is the difference
between the actual cant provided and the theoretical cant
required for such a low speed.
• The limiting values of cant excess have also been prescribed.
Cant excess should not be more than 75 mm on broad gauge
and 65 mm on meter gauge for all types of rolling stock.
43. Design Criteria for
Railways
Cant gradient and cant deficiency gradient
• These indicate the increase or decrease in the cant or the
deficiency of cant in a given length of transition.
• A gradient of 1 in 1000 means that a cant or a deficiency of cant
of 1 mm is attained or lost in every 1000 mm of transition
length.
44. Design Criteria for
Railways
Rate of change of cant or cant deficiency
• This is the rate at which cant deficiency increases while passing
over the transition curve, e.g., a rate of 35 mm per second
means that a vehicle will experience a change in cant or a cant
deficiency of 35 mm in each second of travel over the transition
when travelling at the maximum permissible speed.
45. Design Criteria for
Railways
Centrifugal Force on a Curved Track
• A vehicle has a tendency to travel in a straight direction, which
is tangential to the curve, even when it moves on a circular
curve. As a result, the vehicle is subjected to a constant radial
acceleration:
Radial acceleration, g = V2/R
where V is the velocity (meters per second) and R is the radius
of curve (meters)
46. Design Criteria for
Railways
• This radial acceleration produces a centrifugal force which acts
in a radial direction away from the center. The value of the
centrifugal force is given by the formula:
Force = mass × acceleration
F = m × (V2/R) = (W/g) × (V2/R)
where F is the centrifugal force (tonnes), W is the weight of the
vehicle (tonnes), V is the speed, (meter/sec), g is the
acceleration due to gravity (meter/sec2), and R is the radius of
the curve (meters).
47. Design Criteria for
Railways
• To counteract the effect of the centrifugal force, the outer rail of
the curve is elevated with respect to the inner rail by an amount
equal to the superelevation.
• A state of equilibrium is reached when both the wheels exert
equal pressure on the rails and the superelevation is enough to
bring the resultant of the centrifugal force and the force exerted
by the weight of the vehicle at right angles to the plane of the
top surface of the rails. In this state of equilibrium, the
difference in the heights of the outer and inner rails of the
curve known as equilibrium superelevation.
