What type of flowers or rose bush should I plant next to sidewalk?

From parking on your lawn, my neighbor was advised by our city to place boulders along the area, you could then plant any bush in between each boulder or behind each one. Or possibly a tall grass plant that requires little maintenance. You could Google entering your zone, sun or shade, or partial sun/shade and privacy hedge and see what comes up.

Honeysuckle bushes make a great natural fence. Plant the bushes about 4 feet apart and use a heavy duty plastic coated laundry line to string between them for the vines to fill in the space between. They flower twice a year and depending on the space and your taste will need to be tidies up now and then.

Do you want perennials bushes or evergreens?

As BJ mentioned above, alternating large rock with whatever plants you use will work. I live in zone 6 also and have privets with rocks along one side yard. I planted small hostas among the rocks at the bases of the privets. I've also used butterfly bushes as a border. Roses was would work but you might want to go for a bush variety. You can just make a small fence (pallets would work) or buy some wire fencing borders. It's all about making the boundary visible. You could even use trellises space out (or connected) and growing climbing plants on them (avoid trumpet vines -- they are incredibly invasive). Your lighting will also help determine what you can plant.

Home Dpt, Lowes, Dollar Stores, Garden Centers, etc have great cheep low profile, cute fencing. Even just a couple fan shaped trellises stuck a little less than a cars length apart. They don't have to be very tall. Stick a series of plastic lattice again a little less than a cars length apart. Use anything cheep to drive into the ground to attach/secure the lattice. Hang seasonal/holiday thingies from the Dollar Store, on the barrier of choice. Just start out with a bucket of sand with a stick with decorative stuff on it, again, spaced just far enough apart that drivers get the hint.

Knock out roses are very pretty and low maintenance. Think twice about butterfly plants. They are caterpillars first, and ate a lot of my daughters plants!

Here is a story for you if you have your heart set on roses. I replaced texas privit that was growing in front of my front porch, while it was nice for privacy, I did not care for it. I replaced with 3 rose bushes, a cream, yellow and pink. The cream and yellow I purchased from a local rose farm and paid big bucks for. The pink was a $6.00 Home Depot special. Guess which one grows the fastest, produces more blooms and less prone to rose problems? The $6.00 Home Depot special. I do nothing to them except feed when necessary, deadhead as blooms become spent and my gardener cuts back once a year in the late winter. They are ready to pop and I will have roses for Easter and will bloom continually into the winter months. I always have out of state visitors taking photos of my roses on Christmas and New Year's Day. Something for you to possibly consider.

Knock out roses! No viruses, no work. Beautiful. Don't know about your time zone.

A quick solution would be a native grass like switchgrass (Panicum). 'Cloud Nine' is a really tall one (5'+) and might be the most imposing. Plant in groups of 3, like a triangle, for interest and depth instead of a straight line. Their clumps will get larger over time and may eventually need to be divided . Do not plant Miscanthus (maindenhair grass) as it is highly invasive and is on the invasive list in Connecticut. Lots of choices for you - try talking to the Master Gardener's Group in your county. FYI, sadly, knockout roses now have a serious disease problem.

the cement blocks with the 2 big holes in them? make a short fence using those and poles. you might have seen a similar type of barrier at spring pop up garden shops..space them so a car won't fit between them.