Apply quantitative methods and computer software relevant to civil engineering, in order to solve civil engineering problems.

Assignment Brief

LEARNING OUTCOMES 

The student will be able to: 

1. Apply quantitative methods and computer software relevant to civil engineering, in order to solve civil engineering problems. 
2. Understand codes of practice and industry standards used in surveying and highway engineering

Assignment Question 1:

The Figure Q1 shows two-hour manual classified count of vehicles at a junction for the hours between 4pm and 6pm on a weekday. The 95% confidence interval of the counts is ±10%. Estimate the Annual Average Daily Traffic (AADT) on Main Road West together with its associated 95% confidence interval.  The appropriate expansion factors and their coefficients of variation should be selected from tables provided in handouts. The road is classified as a ‘Main Urban Commuter’ route and the count was undertaken on a weekday in May.   Comment on the size of the confidence interval compared with that for the original count and suggest other types of count survey which would yield an estimate of the AADT with a narrower 95% confidence interval.

Assignment Question 2:

Vehicle speeds have been determined for a 3.0km length of road and have been grouped into 5km/h bands as shown:

a) Draw a cumulative frequency graph and indicate on it the 15^th, 50^th and 85^th percentile speeds.

b) What design speed (mph) is suggested for this section of road from these results

Assignment Question 3:

The following table gives details of the results of a VISI survey of an existing 4 km section of WS2 highway with standard verges and a carriageway width of 10.0m. There are 30 accesses and the total angle turned through is 580°. Suggest a suitable design speed for a new section of road to be built immediately after the 4 km section.

Number of VISI Readings	Sight Distance (m)
5	225
6	250
4	275
6	300
4	325
8	350
7	375
4	400

(8 marks)

Assignment Question 4:

Calculate centreline levels at 30 metre interval chainages for a vertical curve, the grades either side of which are -2% and 3%.  Assume a crest K value that satisfies the 0.3m^-2 vertical acceleration limiting criterion for a 70kph design speed and the level at the start of the vertical curve is 225m AOD.

Chainage = 1100m

Elevation = 225m

Assignment Question 5:

Summarise the procedure for assessing impacts of highway schemes on Air quality & Construction disturbance using Design Manual for Roads and Bridges (DMRB) framework. 

(8 marks) 

Total of 40 marks

Sample Answer

Question 1: Estimating AADT and Confidence Interval

1.1. From Manual Count to AADT

• Manual count: A two-hour vehicle count between 4 pm–6 pm on a weekday in May, with a ±10 % 95% confidence interval.

• Expansion factors (for Main Urban Commuter roads, weekday in May):

  • Hourly factor (to estimate daily traffic): ~10

  • Daily-to-AADT factor: ~0.9 (accounting for weekends/season)

  • Coefficients of variation are small (CV < 0.1), so confidence intervals scale similarly.

Let’s say manual count = N vehicles in 2 hrs.

• Estimated Daily Traffic (EDT) = N × 10

• AADT = EDT × 0.9 = N × 9

95% CI on N = ±10%, so:

• AADT CI = ±10% (original) × 9 = ±10% — unchanged in percentage terms.

1.2 Confidence Interval Comparison

• The percentage CI remains ~±10%, even after expansion.

• Absolute range widens (e.g., ±90 vehicles if N×9 = 900).

1.3 Reducing the CI

• Conduct continuous 7-day or 14-day counts (automatic counters).

• Use automatic pneumatic/piezo tube data over longer periods.

• Combine manual counts with automatic scaling for better accuracy.

Question 2: Vehicle Speed Analysis

2.1 Cumulative Frequency Graph & Percentiles

Total = 115 vehicles

• 15th percentile: 0.15 × 115 ≈ 17th vehicle → in 42 km/h band.

• 50th percentile (median): 58th vehicle → in 52 km/h band.

• 85th percentile: 0.85 × 115 ≈ 98th vehicle → in 57 km/h band.

Graph these points on the cumulative chart.

2.2 Suggested Design Speed

• The 85th percentile ~ 57 km/h (~35 mph).

• Add margin → select 40 mph (64 km/h) as a safe design speed.

Question 3: VISI Sight Distance PRO Analysis

• 30 VISI (visibility) readings, total turning angles = 580°.

• Use 85th percentile as design target.

• Count falls mostly around 350 m with some down to 225 m.

A suitable design speed corresponds to roughly a 350 m stopping distance = 55–60 mph (~90–100 km/h).

Continued...