Jan made some narrow grass splines. They have trackside in their name. I have used them before myself and they look pretty good.
Check out these:
JVC(W)Grass#1 trackside A,<kuid2:328583:3522:2>
JVC#(Gr1) Trackside spline A,<kuid:328583:20247>
JVC#(Gr1) Trackside MESH lib. I,<kuid2:328583:20248:1>
JVC#(Gr1) Trackside spline C,<kuid:328583:20251>
JVC#(Gr1) Trackside spline B,<kuid:328583:20255>
JVC Grass 408 Dry trackside,<kuid:328583:3601>
JVC Grass 409 Dry trackside,<kuid:328583:3607>
JVC Grass 406 Dry trackside,<kuid:328583:3591>
JVC Grass 405 Dry trackside,<kuid:328583:3570>
JVC(S2) Ground cover #7 Grass group trackside,<kuid:328583:4065>
JVC(S2) Ground cover #8 Typhia Grass group trackside,<kuid:328583:4068>
JVC Grass 403 Dry trackside,<kuid:328583:3557>
JVC Grass 404 Dry trackside,<kuid:328583:3563>
JVC Grass 402 Dry trackside,<kuid:328583:3549>
CaddyLars Grass#5d green trackside,<kuid2:328583:3473:1>
CaddyLars Grass#6d dry trackside,<kuid2:328583:3477:1>
CaddyLars Grass#5d green trackside,<kuid2:328583:3481:1>
CaddyLars Grass#5d green trackside,<kuid2:328583:3485:1>
CaddyLars Herbs#1d Dry trackside,<kuid2:328583:3469:1>