Bituplaning a low friction phenomenon where non-ABS emergency braking is carried out on new bituminous road surfacing

1. “Slippery When Dry”
The facts and the f(r)iction surrounding dry
negative textured surfacing (NTS)
John Bullas PhD MIHT MIAT FGS
Research Consultant
Atkins Ltd,
Winchester
john.bullas@atkinsglobal.com

2. Low Dry Road Friction:
Ancient History?

3. Dry friction in the 1930’s
Low dry friction on loose surface dressing (1931)

4. Tyre/Road Temperatures
(Zipkes 1944)

5. Excess asphalt gives lower
dry friction (Switzerland 1944)

6. 1944 v 2004!
“On some road surfaces, the
melting point of the
binder….( the bituminous layer)
…may be reached before that of
the tread rubber, in which case
the slipping co-efficient will have
a different value from that on
which the rubber melts first”

7. More modern times ….

8. Arrival of
Negative Textured
Surfacing : NTS

9. Skid Testing to Measure Dry Friction

10. ABS v NoABS
DRY ROAD
Worn Surface
No Texture

11. Three Phases
(A, B & C) of
a Skid test:
Black- ABS on NTS
Red NoABS on NTS

12. Variation in “Typical” Skid Tests

13. Slippery DRY new HRA
on the M4 - 13 dead (1984)
M4 Wet
M4 Dry
M4 Dry µ=0.44
Typ. Dry µ=0.75

14. NTS: Negative Textured Surfacing

15. Slippery DRY Porous
Asphalt (NTS) Netherlands 1990’s
NoABS
ZOAB
NoABS
“HRA”
ABS
ZOAB

16. NoABS for P.A & Dense Asphalt
Average Braking Coefficients from Bartlett & Fonda (Bartlett and Fonda, 2003)
Typical deceleration figures for PA and Dense Asphalt from Fafié (Fafié, SURF 2004)
6.77 m/sec2

17. That Slippery dry SMA
in Derbyshire!
Pebley Reservoir, Derbyshire, 20th August 2001, skid tests revealed dry Mu
values of 0.496, 0.478, 0.48*. These results were “significantly below what…
would expect for a dry flat road surface“. A typical value in these
circumstances would be 0.7 to 0.75** ”
Car Top, Derbyshire 18th July 2001 skid tests revealed damp road Mu values of
0.519, 0.506, 0.532 & 0.546*. These results were considered “markedly lower
than …expected”
On 25th July 2001, a further skid test was carried out in the same position with the
surface dry …..still some 20% lower than might be expected on a dry flat road,
despite being on an uphill gradient. “. A skid test was carried out on the A621 hot
rolled asphalt. At this site, the Coefficient of Friction was 0.696** considered
“much closer to the value expected”.
New Dutch Porous Asphalt (PA) was delivering 0.55* and New Dense Asphalt
0.71** as reported in 1997 at an International Conference on PA

18. What was not well publicised…..
• The first crash had no witnesses, the casualty was
discovered fatally injured later, no sign of skidding, no marks
on the road, single vehicle fatality (motorbike)
• The second crash involved a vehicle where adaptation for a
disabled driver prevented simultaneous braking and
steering. This fact was pivotal in the outcome of the crash.
• Low dry friction was measured at both locations but was not
important with respect to the dynamics of either crash….
• Don’t let these missing facts get in the way of a good story
for the “technical” press who put the fear up everyone!

19. What is TYPICAL
and what is UNACCEPTABLE
DRY friction?

20. Typical Dry Friction (Opinion)
M4 DRY
1.1+
1.0
0.9
0.8
0.7
0.6
0.5
0.4
<0.3
25%
20%
15%
10%
5%
0%

21. Typical Dry Friction
UK: Multi Vehicle Multi Surface Tests
M4 DRY

22. Typical Dry Friction
HRA
HRA
M4 DRY

23. ‘Typical’ Dry Versus
Wet Investigatory Levels?
0.6 -0.8?
Typical
Dry
Friction

24. NoABS Dry Friction on NTS
HRA
NTS
M4 DRY

25. Bituplaning Dry Friction
Versus Wet Investigatory Levels?
0.4-0.5?
Bitupl.
Dry
Friction

26. Summary: Field
and Laboratory
Tests

27. ABS Dashes… Why?

28. Momentary Low ABS Dry Friction

29. 1000fps NoABS on a PTS:
hyperlink

30. NoABS on a NEW NTS:
The ‘Bituplaning’ Phenomenon
The influence of sliding speed on
Adhesion and Hysteresis (Li et al., 2003)
hyperlink

31. ABS v NoABS
in Infrared with
thermal
data stored as
grid

32. Researcher: ABS PTS

33. Researcher: NO ABS NTS

34. ABAQUS F.E. Modelling
NoABS Wheel Skid – Trial run
ABAQUS Analysis by Dr. M.H.R.Ghoreishy,
Iran Polymer and Petrochemical Institute
PO Box 14965/115 Tehran, Iran
120°c
80°c

35. Is melting causing
the ‘Bituplane’?......
NTS
PTS
NoABS Dry Tests

36. Fluorescence Microscopy
Of latex modified bitumen film
Before and after Skidding
Tests by

37. DSR Tests by

38. De-Oiling @13m/sec shear?
M4 DRY

39. Critical Speed
(loss of control)
VC3000 DAQ Output TRL Test 003 10:35
-150
-100
-50
0
50
100
0 5 10 15 20 25 30 35 40
Time (seconds)
SpeedKMH/AngularRate
(deg/sec)
-1.2
-0.7
-0.2
0.3
0.8
Acceleration(G)
AngularRate (deg/sec)
Speed (kph)
Lat Accel (G)

40. Grip/Slip Characteristics
Braking co-efft. Versus
Wheel Slip (Veith, 1998)

41. Summary:
Analysis and
Interpretation

42. Analysis – Data point extraction
Problem with Internally
Smoothed Skidman Data

43. Resolution: Recorded
versus Extracted
Average Good / Peak Bad

44. Peak / Slide
Ratio for
NoABS NTS
Still OK to
Estimate
NoABS
from ABS?

45. Peak Deceleration– little difference

46. Average Deceleration

47. NTS Statistically better and worse
Better for New cars = ABS and better secondary safety (SRS etc)
Worse for Old cars = NO ABS, poorer safety, younger less experienced drivers?

48. Other Factors to Consider

49. “The nut behind
the steering wheel”…..

50. When Wet: (NO) Change in
Driver Behaviour

51. ….And only Fatal Crashes get
Investigated Properly (1% of total)
…. Nothing reported as
nothing looked for?

52. Will This Sign Save
our Corporate Skins?
…..if it is slippery when dry?

53. When Slippery and Wet: (NO) Change
in Driver Behaviour plus few see warning signs

54. Something like
this might not
either if we are
providing a
surface with
known
“problems”
Transl.: “New Road Surface – Longer Braking Distance”

55. Saying: “The DRY Friction
is no worse than if the surface
was wet”…
• ……doesn’t make sense as we don’t slow down in the wet anyway!
• Do drivers modify their behaviour when friction is commonly known to be
compromised in the wet?
• Typically NO

56. Does Low Dry
Friction on Negative
Textured Surfaces
Matter?

57. Yes it Could Matter….
• Measurements taken from crash scenes have been shown to be significantly different
for NTS surfaces : Lower dry friction without ABS, Higher dry friction with ABS (Estimation
of NoABS from ABS)
• ABS braking can also be influenced by NTS surfaces (rel. to ABS system?)
• Bituplaning may be a combination of changes in the binder film AND the fundamental
frictional differences between NTS and PTS surfaces
• Drivers make little allowance for more slippery wet roads, and don’t see wet skidding signs
so why should we expect any allowances on DRY roads which can be smoother and
quieter than what they replaced?
• 99% of crashes are not properly investigated so any possible role of “bituplaning” in
crash outcome is not seen or is severely underestimated
• A “slight” injury scenario can easily become a fatal if the occupant is 80 and not 18!

58. Thanks for listening,
any questions?