Past exam questions Flashcards
Describe the Accident by Accident analysis
- based on the history of crashes
- dependent on the number of reports
- utilizes the severity categorities, movements and vehicle type
Why do we use PV? what is the sensitivity of the discoutn rate and what is the impact of the discount rate on infrastrucutre?
Discounting to present value enables a standardized approach for evaluating the future benefits/savings of the investment.
The treasury currently advises a 6% discount rate for evaluating the present value. The sensitivity of this rate hinges on treasury inflation estimates which are between 1-2%. Having lower discount rate increases the PV and vice versa.
Why do we use an incremental BCR?
indicates whether the incremental costs of higher project alternatives is justifiable by the benefits. Conversly, also indicates whether a lower cost alternative or an option that realises more benefits is a more optimal solution.
Define externalities and give 3 examples
relevant costs and funds not within the domain of the funding authority but should be included in the appraisal. eg social cost of crashes.
1) benefits with monetary values derived from the market place
2) benefits not given any monetary value
3) benefits not given any monetary value due to being hard to establish a standard value.
Suggest a third alternative design
Strucutral asphalt-> modified aggregate base course -> cement stabilised subbase and subgrade
1) low risk solution, provides numerous benefits such as durability and rutting resistance
2) modified aggregate on top of cement stabilized is a shear resistant way to reduce rutting and water infiltration.
3) Cement stabilized on top of subgrade provides compaction on the upper base
4) support the asphalt layer.
Provide 2 additional options
change the base course to modified aggregate reduces shear
addiing foamed bituminous basecourse because it is a low risk option for high traffic volume roads.
What is the crash trend adjustment factor
factor based on traffic growth rate and posted speed limit
Describe method C
- Uses both historical and the typical crash rate for the site
- enables analysis for sites with no crash history, existing for more than 3 years with no fundamental change and the site is assessed to have a high crash risk.
Describe the simplified priecures analysis methods, give an example.
designed for the appraisal of low cost and low risk activiites, where each procedure stands alone. eg road renewals
Describe tanglibe and intangible effects
tangibles with standard monetary value eg VOC
intangibles with standard montary value eg CO2
intangibles with no standard monetary values eg visual amenity
Draw the diagram for how laser technologies mesure rutting and roughness
refer to doc
explaing the difference between macro texture and micro texture with the aid of a diagram
refer to doc
Why is it not good to have a cement stabilised layer as a base course?
extra care in the mixture to ensure variability of the materials is minimised. Otherwise leads to reflection cracking and allows moisture ingress
Why is it not a good idea to have a cement stabilized layer over subgrade
the layer will fail in shear, allowing water or moisture to infiltrate the subgrade and the layer as well?
describe why rutting is an important conditions
affects vehicle handling, water ponding, affects road safety, reflections driver perception
