February 2008 Moor Value Ltd International Conference on Road Safety in Africa A Low-tech Approach to Urban & Rural Safety Engineering Clive Sawers MA.

Clive Sawers MA MICE CengTraffic Engineering Consultant

Mini-roundabouts – A Definitive Guidewww.mini-roundabout.com

February 2008 Moor Value Ltd

International Conference on Road Safety in AfricaA Low-tech Approach to Urban & Rural Safety Engineering

Current trends in urbanCurrent trends in urban& rural road safety engineering& rural road safety engineering

The African PerspectiveThe African Perspective

byClive Sawers M.A. M.I.C.E. CEng.Traffic Engineering Consultant, UK





Additional Material for viewing

This is the presentation that I made at Abuja on Monday 18 February 2008

I have added explanatory text to the slides to complement the text, images and graphics that you will see as you progress through the presentation. In general I suggest that you read first these text additions that appear on most of the slides; they are all in black (or occasionally white) Times New Roman font style.

This presentation is offered for download free but must not be copied, amended or otherwise altered in any way without the express permission of the author. Similarly the advice given is based on experience but no liability can be accepted for any errors or omissions. Design Engineers and any others who wish to make use of the advice given in this presentation must satisfy themselves that it will be applied appropriately and should apply all precautions.

Clive Sawers MA MICE CEngMarch 2008





The Culture of Road Safety – the 5 Es!

• Education• Children road safety education• Driving instruction and tests

• Engineering• Better design – roads &

layouts• Better design - vehicles• Safety audits

• Enforcement• Police presence/FRSC• Cameras

• Emergency Services• Fire & Rescue• Ambulance

• ENTHUSIASM!• Road Safety Professionals

• Conferences & Seminars

• Publications

• Other training, liaison, forums etc…

• A PASSION for Road Safety

During the course of the conference there were several “Es” added to the list! But the three main ones of road safety are Education, Enforcement and Engineering. This presentation is based mainly on Engineering.





In this presentation I shall demonstrate that:

• In the urban environment• continuity of footway/sidewalk important

• Roundabouts create safe intersection facilities

• Roundabout splitter islands work for pedestrians and cyclists

• extending the splitter island creates a long median/refuge

• Speed tables can fill all the gaps between roundabouts if needed

• In the rural environment• Single two-way main roads with roundabouts can be safe

• And what their risks are

• Divided highways can be made safe• And what their risks are

• Incomplete routes comprising both divided and two-way roadways • Special problems to be avoided





What’s wrong with signals?

• Signals and pedestrian facilities are not as safe as they should be• High severity ratio (proportion of accidents with serious injuries)• Turning or right angle crashes (usually serious)• Pedestrian accidents feature at signals usually serious• Turns often banned – U-turning impossible

• Costs• May cost slightly less to install signal than roundabout initially• Shorter life-span• Ongoing maintenance

• Failures• Breakdown• Power supply – these are serious problems here… [in Abuja & the rest of Nigeria

so I understand]





Pedestrian signal crossings (not at intersections)

• Becoming more sophisticated• Require regular maintenance• Require some enforcement• Safety record improving but• Injuries still severe• Subject to breakdown• Subject to power failure• Pedestrians don’t wait

An example of the typical behaviour at most UK pedestrian signals





Low-tech?

• Roundabouts and physical layouts safer• Fewer crashes per 100M vehs

• Crash severity low

• Pedestrians accidents rare

• But often not perceived to be safer

• Cost• Usually a little more expensive to

construct

• Almost maintenance free!• Minor crash damage• Feature maintenance• Resurface approaches & circulatory

roadway – 15 year cycle

• Pedestrian refuges/central medians safer than signal crossings

The concept at this site was to ensure that once built there would be very little to maintain and that speeds would be constrained by the geometry and the slower vehicles.





Are signals really safe?

A serious problem especially in wet weatherA serious problem especially in wet weather

A recent installation in my home town, Newton Abbot. It is an ugly poor slow installation at which pedestrians will not wait. I fear for the future accident record here





Problems with power failures

XA failed signal installation in Abuja controlled by a police officer. This is a common occurrence in the city. The failure was resulting in overshoots from the lower right as indicated in the next slides.





Problems with power failuresAlmost nothing to indicate to drivers that there is an intersection here at all!

The one signal head arrowed hardly shows and the street lights (perfectly) line up straight through the intersection.

I have suggested relocating two of the street lights, duplicating the signal heads and adding some road markings…one or more rumble areas as shown





Problems with power failures





Is this a pedestrian-friendly environment?

An illustration of the roads in Bangkok where it is virtually impossible to get anywhere on foot. These footbridges are OK but not for the disabled. Not a pedestrian-friendly environment.





Basic needs for pedestrians

• ALONG - normal street• Footway/Sidewalk provision• Continuity• Wheeled pedestrian vehicle

friendly• Ample crossing points with

drop-kerbs• Clear of obstructions

temporary or permanentincluding missing links!

Halkidiki,Greece

I came across this appalling gap at a seaside resort in Greece. They would argue that this is not a footway/sidewalk but it was certainly used as such.





Basic needs for pedestrians

• ALONG - quiet street (<100 veh/hr)• Safe to mix with traffic

• Ensure low speed

• Direction of traffic flow clear

• Lots of scope to providesense of place

A typical street in the UK where traffic volumes have been reduced such that pedestrians can more freely enjoy the space. The footways alone are much too narrow for the pedestrian volumes at peak pedestrian times.





Pedestrian Safety - Crossing

• Signal junctions no guarantee of safety

• Red/green man has been shown not to enhance safety

• Neither do guardrails• For pedestrians to get the best

and safest deal they need: • To cross a single traffic stream

at a time • Speeds to be very well

controlled • Not normally to have right of way

• Refuges essentially safe• Refuges & speed tables even

better where appropriate.A typical layout near bus stops in a UK town. Pedestrian refuges perform a safe function at thousands of such locations





Borehamwood, Herts, UK – “before”

A typical shopping street in the UK. This was changed dramatically as per the next two slides. See New Life for Main Roads website





Borehamwood – “after”…

Note mini-roundabout, single lane divided highway and speed table





Borehamwood – “after”…





Speed table using H-humps





H-hump SW London

One of too few H-humps in the UK. These are difficult to build but potentially very effective. They are designed to allow all vehicles to cross at around the same speed by lengthening the climb for heavier vehicles that usually have much harder suspension,





Crashes at urban/rural intersections (UK)

Fatal & Serious Slight

Here the roundabouts shows up as the safest intersection type in both urban and rural environment





Some urban roundabouts

A gateway roundabout in France – a good way to control speeds entering a village.






This is a high capacity small roundabout in the UK. It is the sort of scheme that could replace many 3-arm signal installations in Abuja and doubtless elsewhere in the country and continent.











A mini-roundabout at a crossroads; the central island is larger than the UK standard but this is often necessary to achieve the required deflection of otherwise straight paths. The complex road marking at the centre is not visible to drivers – a single uniformly painted area is preferred.





Selection of (mini-) roundabout sites

• Intersections of (usually) 2-way roads • where some turning space can be added (if needed) by:

• widening corners or • narrowing approaches

• Mostly 3-way urban junctions• Some 4-way junctions • Double and multiple 3-way junctions • Current control may be signals or priority• Not normally new junctions for mini-roundabouts

• Side-road flow Side-road flow 10% of main road 10% of main road flowflow This last criterion is very important;

roundabouts should not be used where the side road flows are too low…





Site Selection factors

• Getting “knotted up” at peak periods • mainly priority intersections but • can include signals (esp. when not working)

• Long queues getting on (or off) • History of crashes involving:

• turning • speeding • pedestrians

Many 3-arm intersections in Abuja get “knotted up” when the signals fail.





(Motor-) Cycle Safety

• Nodes (Mini-) roundabout• Drivers MUST recognise presence of roundabout in good time• Drivers’ perceive the need to yield on entry• Design to incorporate speed reducing features• Narrow approach lanes more (m-) cycle-friendly than one wide lane

• Links (Single lane divided)• Pedal cycles mostly keep up with traffic• Special form of H-hump safe for all two-wheeled vehicles

Motor-cycles feature in crashes at roundabouts – they are very vulnerable. Ensuring that entry speeds are well controlled helps to reduce the risk.





Conflicts at mini-roundaboutsCrossing conflict

Merging conflict

W E

S

N

3-way mini-rbt

crossing conflictsmerging conflicts

straight traffic movement

with crossing conflicts

3

1

3

Crossing conflict

Merging conflict

4-way mini-rbt

crossing conflicts

merging conflicts

straight traffic movementswith crossing conflicts

20

84

4-way double-mini-rbt

crossing conflicts

merging conflicts

straight traffic movements

with crossing conflicts

18

8

4

W

It is at the crossing points (red) that most crashes occur, some may be serious.

At right-angle crossroads these usually are serious highlighting the need for good deflection.





Accident types at 3-arm mini-roundabouts

Single vehicle

Merging

Other Pedestrian

Shunt

Crossing

Source: Accidents at mini-roundabouts - TRL

The accident types at 3-arm (and 4-arm next graph) are illustrated here. It is the crossing accidents that are most influenced by correct deflection. The remainder of the accidents are associated with poor entry configuration – little or no change from the previous layout.

At my sites the pattern was different, I had few pedestrian, shunt, merging and single vehicle accidents. The crossing accidents featured at those sites where I was unable for topographical reasons to ensure satisfactory deflection.





Accident types at 4-arm mini-roundabouts

Other crossing

Other

Single vehicle

Shunt

Merging

Pedestrian

Right angle

Source: Accidents at mini-roundabouts - TRL

Crossing accidents dominate at crossroads; poor entry layout and lack of deflection are common at such sites.

Deal with these issues at the design stage and these installations should be reasonably safe.





Mini-roundabouts at X-roads

Method of ensuring thata crossroads mini-roundabout has sufficient “ahead” deflection – crucial.

Vehicle paths must be curved to the settings shown 60m radius or less.





Mini-roundabouts at X-roads

Example of a design with a large enough centre to deflect all vehicles – similar to German compact roundabouts.





Safe scheme at a crossroads

Just 1 slight injury accident in 17 years!





Joining it all up…

• Nodes• (Mini- ) roundabouts at the main intersections• Minor intersections restricted turns

• Links• Add central median if sufficient width• Otherwise refuges where possible• Speed Tables at frequent intervals





Rec.P

School

P.O.

Developing your scheme

Click your way through the elements as they are added to complete the infrastructure needed to ensure as safe a community as possible; these are:Footways/sidewalksMediansGatewaysMini-roundaboutsTables





A common layout in Abuja





A common layout in Abuja

Click through to show the vehicle paths and conflict area followed by pedestrian crossing lines.

Note that pedestrians have to cross some 2-way streams.





A better layout

The mini- or smallroundabout as illustrated here is apowerful, cheap and very safe tool.

Turning is easy and U-turning, needed often, is available. Pedestrians cross with little difficulty. See Mini-roundabouts – A Definitive Guide.

Again, click through the vehicle and pedestrian movements as they illustrate how all the conflicts are handled and how pedestrians cross uni-directional flows, a much easier and safer task.





Layout for divided highway intersectionsThis roundabout would have:This roundabout would have:

• Very high capacityVery high capacity

• A good safety recordA good safety record

• Pedestrian crossing pointsPedestrian crossing points

• Minimum maintenanceMinimum maintenance

• A central feature, maybeA central feature, maybe

Cost ~ N1M

There are many intersections like this in Abuja so this is offered as a standard layout to permanently replace the layouts currently controlled by traffic signals, most of which were inoperative at the time of my visit.





Yarnton Way (SE London)

• The Concept• Reduce 2-lane divided highway to single traffic lane retaining median• Cycle lane/track added separated by hatching• Roundabouts at key intersections• Additional crossings where school pupils gather





Single Lane dualling + roundabouts

Note the large overrun area to ensure adequate deflection and the use of the splitter island for the cycle route.





Single Lane dualling + roundabouts





Rural Main Roads

• UK TD 9/93 Highway Link Design is 70 pages!• is available on the internet• Covers single and divided highways

• For busy inter-urban routes plan for divided highways• Grade separated interchanges• Continuous central reservation

• with barrier unless very wide• NO crossovers except for emergency use (must be closed)

• All roadside structures to be protected with crash barriers• Provide adequate stopping facilities

• Laybys every 500m or Continuous hard shoulder • Service areas

• Drain to outside unless sharp bend – slight adverse crossfall better than changes in crossfall from side to side





Rural two-way Roads

• Use well designed roundabouts for main intersections• Avoid traffic signals• Avoid crossroads & T- intersections

• Along links:• Delineate edges well• Provide laybys or other areas to stop• Protect necessary road-side structures• Clear obvious obstructions e.g. trees, rocks to at least 5m.• On mountain routes provide edge barriers• Ensure there is no confusion if parts of route divided highway.• Use prohibitory double white/yellow lines to prevent overtaking

at bends/summits/intersections





Prohibitory white line system





Divided highway or single?Divided highway or single?

This road is 2-way clearly – This road is 2-way clearly – BUT notice the recent change BUT notice the recent change in centre line markings; this is in centre line markings; this is a short length between several a short length between several

miles of divided highwaymiles of divided highway……

This short sequence of slides illustrates the problems of appearance when lengths of divided highways are used with single two-way roads – great care must be taken not to create illusions.





This is (obviously) a divided highway





This road is 2-way (though not obviously so)

Note the unprotected columns (Grand Cayman)





This could be 2-way or part of a divided This could be 2-way or part of a divided highway - WE DON’T KNOW…highway - WE DON’T KNOW…





This looks like a divided highway…

The opposite roadway is over here – or is it???





This is a SINGLE 2-way road!This is a SINGLE 2-way road!The bridge crosses the road and a railway The bridge crosses the road and a railway giving the illusion of a divided highway!giving the illusion of a divided highway!





Rural Divided Highways – Safety Risks

• High speeds• Not suitable for vulnerable users – cycles, pedestrians

• Not safe to cross at grade – provide bridge/underpass/roundabout

• Separate roadways well or provide median barrier, prevent crossing median

• Provide adequate space for running off road but protect drops

• Provide underpasses for wildlife

• Keep above flood plain & design for sand/debris to blow off

Entering the wrong way – risk of head on collision

• Use roundabouts at access slip-roads – very difficult to enter wrong way

• At-grade roundabouts optional but DO NOT USE SIGNALS

• Have sufficient interchanges to reduce risk of drivers reversing (having missed their exit)

• Stopping• Control road-side sales on busiest main roads.





Rural divided highways near Abuja

A dangerous mix of pedestrians andA dangerous mix of pedestrians andhigh speed traffichigh speed traffic

Control of roadside activities needed…Control of roadside activities needed…





Rural divided highways near Abuja

A dangerous mix of pedestrians andA dangerous mix of pedestrians andhigh speed traffic + turning vehicles…high speed traffic + turning vehicles…

Control of roadside crossovers needed…Control of roadside crossovers needed…The problem here is that the road has been constructed without the crucial safety features built in. Relatively costly to add later compared with cost if included in the original design. But this includes overbridges etc that do not come too cheap at any stage.





A solution to remove median crossovers

Using two at-grade roundaboutsnot more than about 3 miles/5km apart

Allow right turns only from any side-roads

Construct central median barrier





A solution to remove median crossovers

One roundabout available to redirect left turnsPartial closures of median gaps possibleBUT very difficult to enforce





A solution to prevent crossovers

One roundabout available to redirect left turnsFULL closures of median gaps possible.May help reduce pedestrian conflict with roadside salesby restricting these to side-roads.

Add 2-way service linkAllow right turns ON





A solution to prevent crossovers

•Safe turning facilities

•U-turning for maintenance/service/emergency

•More land take than diamond interchange

•Longer bridge for accel. Lanes

•Sign routes carefully

Provide an over (or under) bridge for minor road

Add slip roads and small roundabouts

Sign carefully

Prevent crossovers with median barrier





Conclusions – urban roadsConclusions – urban roads

• The tools are availableThe tools are available• (Mini-) Roundabouts(Mini-) Roundabouts• Medians/refugesMedians/refuges• H-humps/tablesH-humps/tables

• Highly relevant for developed countriesHighly relevant for developed countries• As Borehamwood has provedAs Borehamwood has proved

• Even more relevant for developing countriesEven more relevant for developing countries• Low maintenance costsLow maintenance costs• No signal breakdown issuesNo signal breakdown issues• Always pedestrian friendlyAlways pedestrian friendly

• Can be landscapedCan be landscaped• So High-tech or Low-tech?So High-tech or Low-tech?





Conclusions – rural main roadsConclusions – rural main roads

• Use roundabouts where possible on Single Level intersectionsUse roundabouts where possible on Single Level intersections• Protect road-side objects, structures, trees, precipicesProtect road-side objects, structures, trees, precipices• Use Double White/Yellow line system on all single rural roadsUse Double White/Yellow line system on all single rural roads

• Consider divided highway for busier routesConsider divided highway for busier routes• Reduces risk of collisionsReduces risk of collisions• Provides safe overtaking opportunitiesProvides safe overtaking opportunities• Higher capacity & level of serviceHigher capacity & level of service• Provide grade separated interchanges on major divided highwaysProvide grade separated interchanges on major divided highways• Reduce/eliminate crossoversReduce/eliminate crossovers

• Avoid illusions of divided highway when actually singleAvoid illusions of divided highway when actually single

Thanks for listening and participating…Thanks for listening and participating…

Clive Sawers – Moor Value Ltd, UKClive Sawers – Moor Value Ltd, UK

www.mini-roundabout.com

February 2008 Moor Value Ltd International Conference on Road Safety in Africa A Low-tech Approach to Urban & Rural Safety Engineering Clive Sawers MA.

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