Campaign
Top-of-rail friction, measured across three Zurich sections
One August day, three sections, one portable tribometer: what the friction coefficient actually does, lubricated and not.
Question
Does lubrication actually hold the friction coefficient in the target window, on a working network, or only on paper?
The friction coefficient at the wheel-rail contact is not a fixed material constant: temperature, humidity, rainfall, season and contamination all shift it, and the same variability sits behind the wear, noise and rolling-contact fatigue that follow.
Zurich's own weather record shows how far that window moves, across the year and across the decade, so a single measurement never tells the whole story: adhesion needs mapping across sites and seasons.
Traila measured three sites on the Zurich tram network in a single half-day campaign: a downhill curve at Gloriastrasse, a straight section at Rämistrasse, and a straight section at Weinbergstrasse, right before the Leonhardstrasse turn.
What we did
Measured wheel-rail friction at three Zurich sections with a portable tribometer clamped to the railhead
Covered one curve with wayside lubrication, one straight section with only onboard lubrication, and one curve with wayside lubrication switched off
Repeated measurements along each section, inner and outer rail, ten runs per point
Used a Rivelin Rail PRT300 portable tribometer: it clamps magnetically to the railhead, and samples the resulting force at 100 Hz under up to 200 N of load as a freely rotating steel wheel rolls along the rail
What we measured
The top-of-rail friction coefficient at each site, under dry-rail conditions, on one hot August day
The same measurement repeated across a wayside-lubricated site, a site with onboard lubrication only, and a site with wayside lubrication switched off
A one-off measurement on one hot, dry August day; the results should not be extrapolated to other seasons without further testing
- 01
Across all three sites, the friction coefficient stayed within a similar range, lubricated or not.
- 02
The straight section, without wayside lubrication, measured the highest friction of the three.
- 03
A thin oily film was observed across every section tested, whether wayside- or onboard-lubricated.
- 04
At Gloriastrasse, the curve with wayside top-of-rail lubrication, the friction coefficient measured lower where that lubrication reached the rail, and higher where repeated test runs had cleaned it off.
- 05
At Weinbergstrasse, with the wayside system switched off, the inner rail measured a higher friction coefficient than the same rail at Gloriastrasse, where wayside lubrication is installed; the outer rail measured lower on average, suggesting the trams' own onboard flange lubrication reaches the top of the outer rail too.
- 06
Traila recommends a follow-up campaign across different seasons, and more sites on the network, subject to the operator's interest.
A lubrication strategy is only as good as the friction data behind it. Measuring the coefficient site by site, and season by season, shows where conditioning is needed, how much, and what it actually changed at the wheel-rail contact.