The French company Cermex gives 'ledge' as the translation for "trottoir" in this context. There is also a drawing of a box with an strip that forms a narrow ledge of material along the top edges of the box at both sites given below. Then I found a British company that uses ledges as well.

Caisses Américaines Spéciales [see schemata]
Des standards spécialement adaptés à vos besoins: fond semi-automatique, trottoir de gerbage...
http://www.able.fr/plateau-fruits-legumes/cartons-speciaux-a...

Formage d'emballages Display/Prêt à Vendre/Shelf Ready - Formeuse Multi Emballages F550
III – LES REPERCUSSIONS AU NIVEAU DES EMBALLAGES SECONDAIRES
• Barquette (haute, basse, à flancs asymétriques) + coiffe (en U, en croix, intérieure ou extérieure, collée ou non),
• **Barquette à trottoir.**
http://www.cermex.fr/actualites/actualites/33-formage-d-emba...
Forming of Shelf Ready Packaging - F550 Multi-Packaging Erector
III – REPERCUSSIONS ON SECONDARY PACKAGING
• Tray (with high, low or sloping sides) + lid (U or cross-shaped, internal or external, glued or not),
• **Tray with ledges**
http://www.cermex.eu/news/news/33-forming-of-shelf-ready-pac...

Range of machines suitable for various tray designs such as: nestable trays, leak proof packaging, octagonal trays, trays with attached lid, **trays for fruits and vegetables with ledges** and for strengthened corners, etc
http://www.adpak.co.uk/trayloading.htm


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Note added at 4 days (2007-12-03 14:33:38 GMT) Post-grading
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You're welcome, Kimberly, and thank you :-)