1. Applicability of a Screening Model
at motorway and roundabout sites
in Ireland.
Rajiv Ganguly
Una Budd
Brian M. Broderick
Bruce D. Misstear.
Department of Civil Engineering
University of Dublin, Trinity College

2. Overview
v Objectives
v Screening Model (DMRB)
v Application of DMRB at motorway and roundabout
v Comparison of two versions of DMRB (1999 & 2003)
v Modification of roundabout as per DMRB-2003
v Speed versus concentration characteristics.
v Conclusions

3. Overall Research Objectives
Ø To predict vehicular pollution by using a
variety of atmospheric dispersion models.
Ø To perform studies by applying a variety of dispersion
models to different road configurations to ascertain
the applicability of each model.

4. Overall Research Objectives
Ø To carry out inter-comparison of modelled data
obtained by using a variety of dispersion models by
performing statistical and graphical analysis.
Ø To recommend suitable atmospheric dispersion
models for vehicular pollution prediction in Ireland.
Ø To compare the monitored and predicted data sets
obtained by using a variety of dispersion models by
performing statistical and graphical analysis.

5. Background Information.
n Road traffic is one of the major sources of air
pollution and technological and transport policy
measures have been developed for reduction of its
impacts.
n Ambient air quality standards have been set to keep
pollution levels in check.
n Transport sector is responsible for 50% of NOx
emissions and 80% of total CO emissions in Ireland.
n Pollutants considered in study were CO, Benzene,
NOx and PM10. NOx and particulates have severe
health impacts.

6. DMRB Screening Model
Ø Developed by UK Transport Research
Laboratory.
Ø Used for initial assessment of any existing
or planned road programmes.
Ø Estimates vehicular emissions from light and
heavy duty vehicles upto 2020.

7. DMRB Screening Model.
Ø Primary objective is to determine whether
further air quality assessments required.
Ø Model was primarily designed for CO and
assumes that dispersion characteristics of
other pollutants equivalent to those of CO
Ø The model in its simplest forms uses a
series of look up tables based on outputs
from Gaussian Dispersion model. A
spreadsheet version of the model is used.

8. DMRB Screening Model.
Input data for DMRB model (1999) for each
link.
Ø Hourly vehicle flow.
Ø Proportion of light and heavy duty vehicles.
Ø Vehicular Speed
Ø Year
Ø Distance to Receptor.
Ø Background Concentrations.

9. DMRB Screening Model.
Input data for DMRB model (2003) for each link.
Ø The new version of DMRB model (version
1.02, Nov 2003) uses the AADT values as
vehicles per day rather than vehicles per
year.
Ø Introduces a new concept of road type
parameter.

10. DMRB applied on motorway.
Criteria for site selection.
Ø High traffic flows for monitoring purposes.
Ø Traffic flow should be quantifiable.
Ø Site should allow placement of monitoring
equipment near road and in downwind
direction of prevailing wind.
Ø No obstruction between road and
monitoring unit.
Ø Continuous power supply.

11. DMRB applied on motorway.
Other Practical Criteria for site selection.
Ø Proper security arrangements
Ø Permission from the site owners.
Ø Easy accessibility to the site.
Ø The average vehicle speed was assumed to
be 100km/hr at the motorway site.

12. Motorway
Site
Monitoring Unit
M4 Carriageways
(Leixlip)

13. Monitoring Location - Motorway
TO DUBLIN
TO WEST
MONITORING
LOCATION
HEDGE
BUILDING
25m
N

14. Monitoring at Motorway Site

15. DMRB results on motorway (annual averages).
Measured
concentrations
DMRB model
Prediction
Actual
(2)
Calculated
from
annual
mean
1999
version
(2)
2003
version
CO annual
average (mg/m3)
0.32 0.32 0.37 0.39
benzene annual
mean (µg/m3)
- - 0.99 0.54
NOx annual mean
(µg/m3)
32.29 32.29 142.05 80.13
PM10 annual
mean (µg/m3)
15.50 15.50 15.83 17.99

16. DMRB results on motorway.
.
Salient Features.
Ø No substantial difference in CO
concentration by applying both the versions
of the model.
Ø Large reduction in Benzene and NOx
concentration by applying 2003 version of
DMRB
Ø Slight increase in Particulate concentration
using 2003 version of DMRB.

17. DMRB results on motorway.
n Statistical equivalents of Pollutants
Ø CO 8 hr mean=10 x CO annual average
Ø PM10(90th percentile of daily mean)=1.79 x
PM10 annual average.
Ø Maximum annual running mean (benzene)
= 1.102 benzene annual mean - 0.004 .

18. DMRB results on motorway (statistical equivalents).
Measured
concentrations
DMRB model Prediction
Actual
(2)
Calculated
from
annual
mean
1999
version(2)
2003 version
CO 8 hr mean (mg/
m3)
2.56 3.20 3.69 3.90
benzene maximum
running annual
mean (µg/m3)
0.53 - 1.09 0.59
NO2 annual mean
(µg/m3)
19.37 17.09 58.27 15.86
PM10 90th
percentile of
annual mean.
(µg/m3)
22.83 27.75 28.34 32.2

19. DMRB results on motorway.
finding NO2 background from NOx background
concentrations
1. Obtain annual mean background NO2 (background)
and NOx (background) concentrations
2. Calculate the annual mean contribution due to the
road, NOx (road), at the location of interest
3. Convert the NOx (road) to NO2 (road) using the
equation.

20. DMRB results on motorway.
NO2 (road) = ((-0.068 x Ln (NOx (total))) +0.53) x
NOx (road), where NOx (total) =NOx (background) +
NOx (road), and Ln is log to the base e
4. Add the NO2 (road) to the NO2 (background) to get
the NO2 (total) at the location of interest.

21. Roundabout
Site
Monitoring Unit
N6
(Galway)

22. N6/N84 Roundabout

23. Monitoring Location - Roundabout
N84/Headford Rd.
N6
Sandy Road
N6/Headford Rd.
Menlo Rd.
N
25m 15m
Monitoring Unit

24. Roundabout Monitoring Unit

25. DMRB application on Roundabout.
Ø Comparison of DMRB results obtained by
using 1999 and 2003 versions.
Ø Modification of 5 link problem to 3 link
problem is done on basis of traffic flows.
The average vehicle speed assumed was
15km/hr.
Ø Road links combined are (N84 –N6) and
(Menlo and Sandy road) . N6 Dublin road is
third link. For the combined road links
average of the traffic flows is considered.

26. DMRB model
results at
roundabout
site (annual
averages).
Pollutant DMRB model results Measured
Concentration
1999
5 links
2003
5 links
2003
3 links
Actual Calculation
from annual
mean
CO
annual
average
(mg/m3)
2.09 2.25 1.36 0.54 0.54
benzene
annual
mean
(µg/m3)
12.54 4.39 2.53 - -
NOx
annual
mean
(µg/m3)
774.95 283.2 165.04 39.42 39.42
PM10
annual
mean
(µg/m3)
44.91 54.68 36.49 25.50 25.50

27. DMRB results on Roundabout.
.
Salient Features.
Ø No substantial difference in CO
concentration by applying both the versions
of the model.
Ø Large reduction in Benzene and NOx
concentration by applying 2003 version of
DMRB
Ø Slight increase in Particulate concentration
using 2003 version of DMRB.

28. DMRB results on Roundabout.
.
Modification of 5 arm junction to 3 arm junction.
Ø Reduction in CO concentration by 40%.
(2003 version)
Ø Reduction in benzene concentration is 42%.
(2003 version)
Ø Reduction in Particulate concentration by
33%.(2003 version)
Ø Reduction in NOx concentration by
79%(1999 version) and 41% (2003 version)

29. DMRB results on Roundabout.
n Statistical equivalents of Pollutants
Ø As in the motorway similar statistical
equivalents of pollutants were computed
also for the roundabout. Trends were the
same as for annual averages for all the
pollutants except benzene where no
monitoring data was available for the
roundabout site.

30. Pollutant DMRB model results Measured Concentration
1999
5 links
2003
5 links
2003
3 links
Actual Calculation
from annual
mean
CO 8 hr
mean (mg/
m3)
20.93 3.9 13.6 2.86 5.4
benzene
maximum
running
annual
mean (µg/
m3)
13.79 4.83 2.78 - -
NO2
annual
mean (µg/
m3)
193.95 39.65 31.84 19.79 13.09
PM10
90percentile
daily mean
(µg/m3)
80.38 97.88 65.32 39.61 45.62
DMRB model
results at
roundabout
site
(statistical
equivalents).

31. Study of speed versus emission characteristics for new
version of DMRB model (5 links and 3 links).
n Figure 1. Comparison of speed versus
concentration for CO for 5 link and 3 links
model.
0
0.5
1
1.5
2
2.5
0 50 100 150
speed in km/hr
concinmg/m3
from 5 link
from 3 link

32. Study of speed versus emission characteristics for new
version of DMRB model (5 links and 3 links).
n Figure 2.Comparison of speed versus
concentration for benzene for 5 link and 3 links
model.
0
1
2
3
4
5
0 50 100 150
speed in km/hr
concinmicrogram/m3
from 5 link
from 3 link

33. Study of speed versus emission characteristics for new
version of DMRB model (5 links and 3 links).
n Figure 3. Comparison of speed versus concentration
for NOx for 5 link and 3 links model.
0
50
100
150
200
250
300
0 50 100 150
speed in km/hr
concinmicrogram/m3
from 5 link
from 3 link

34. Study of speed versus emission characteristics for new
version of DMRB model (5 links and 3 links).
n Figure 4. Comparison of speed versus
concentration for PM10 for 5 link and 3 links
model
0
10
20
30
40
50
60
0 50 100 150
speed in km/hr
concinmicrograms/m3
from5 link
from3 link

35. Ø For both the motorway and roundabout site the DMRB
model (version 2003) gives a very reduced concentration for
benzene and NOx whereas no substantial difference for CO or
particulates when compared with 1999 version. At the
motorway site model predictions agreed reasonably well with
measured values.
Conclusions
Ø For the roundabout site transforming the 5 link problem
to 3 link problem as per the DMRB manual results in large
reduction of concentration for all the pollutants.
Ø A screening model, DMRB has been discussed and has
been applied at two different road configurations..

36. Conclusions
Ø Irrespective of the modelling approach (3 or 5 links) or
model version (1999 or 2003) employed the predicted
values heavily overpredict the measured concentration.
With the use of 2003 version the level of overprediction
has decreased considerably .
Ø Study of the speed vs. emission characteristics show
that for an average vehicle speed of 30km/hr in a 3 link
model with the 2003 DMRB version leads to very good
agreement between modelled and measured annual
average concentrations of CO and PM10 .

37. Acknowledgement.
n This work has been completed under the
Environment Transport Interface (ETI) project funded
by the ERTDI Research Programme which is
managed by the Irish EPA and forms part of the
National Development Plan.

38. Thank You