HRE terms Flashcards
The cross section of a typical highway has latitude of variables to consider such as:
- The volume of traffic.
- Character of the traffic.
- Speed of the traffic.
- Characteristics of motor vehicles and of the driver
A cross section design generally offers the expected level of service for safety and a recent study showed that:
- A 7.20 meters wide pavement has l8% less accident compared with pavement narrower than 5.50 m. wide.
- A 7.20 meters wide pavement has 4% fewer accidents than the 6.00 meters wide roadway.
- Accident records showed no difference between the 6.60 meters and the 7.20 meters wide pavement.
- For the 6.00 m., 6.60 m. and,7.20 meters wide pavement with 2.70 to 3.00 m. wide shoulder, recorded accident decreases by
30% compared to 0 to .60 m. wide shoulder. And 20% compared with a .90 to 1.20 meters wide shoulder.
is needed in estimating the amount of cut or fill needed for a given strip of roadway.
Cross-sectional data
distance at which a driver of a vehicle can see an object of specified height on ht e road ahead, assuming adequate sight and visual acuity and clear atmospheric conditions.
sight distance
types of sight distances
- Stopping or absoulte minimum sight distance (SSD)
- safe overtaking (OSD) or passing sight distance (PSD)
- Safe sight distance for entering an intersection, Intersection Sight Distance
Minimum sight distance available on a highway at any spot should be of sufficient length to stop a vehicle traveling at design speed, safely without collision with any other obstruction.
It depends on
a. Feature of road ahead
b. Height of driver’s eye above the road surface (1.2m)
c. Height of the object above the road surface (0.15m)
Criteria for measurement
a. Height of driver’s eye above road surface (H)
b. Height of object above road surface (h)
Stopping or absolute minimum sight distance (SSD)
Factors affecting SSD
- Total reaction time of driver
- Speed of vehicle
- Efficiency of brakes
- Frictional resistance between road and tire
- Gradient of road
It is the time taken from the instant the object is visible to the driver to the instant the brake is effectively applied.
total reaction time of driver
It is the time from the instant the object comes on the line of sight of the driver to the instant he realizes that the vehicle needs to be stopped.
perception time
The brake reaction also depends on several
factor including the skill of the driver, the type of the problems and various other environment factor. Total reaction time of driver can be calculated by “PIEV” theory.
brake reaction time
PIEV theory
P - perception
I - intellection
E - emotion
V - volition
is the sum of lag distance and the braking distance
SSD
The distance the vehicle travelled during the reaction time
lag distance
Distance travelled by the vehicle after the application of brake.
breaking distance
The minimum distance open to the vision of the driver of a vehicle intending to overtake slow vehicle ahead with safety against the traffic of opposite direction
minimum overtaking sight distance (OSD)
or the safe passing sight distance
analysis of SSD
lag distance
breaking distance
Clear sight triangle must be free of sight obstructions such as
- buildings
- parked or turning vehicles
- trees
- hedges
- fences
- retaining walls
- actual ground line.
in 1824, he carried out the pioneering work developing steam energy
Nicolas Carnot
in 1804, he designed and constructed a steam locomotive
Richard Trevithick
in 1814, he produced the first steam locomotive used for traction in railways
George Stephenson
in 1825, Recorded first public railway in the world was opened to public, between
Stockholm and Darlington
in 1833, First railway line in USA between
Mohawk and Hudson
in 1835, First railway in Germany was opened
from Nuremberg to Furth
in 1875, he promulgated a Royal Decree directing the Office of the Inspector of Public Works of the Philippines to submit a general plan for railroads on Luzon
King Alfonso XII of Spain