In my opinion, trikes are safer than bicycles. They are more readily noticed by drivers (perhaps because of their novelty), tend not to fall over (three wheels), and are very stable during high speed cornering. But a few upgrades can help improve this:

Mirrors:

Put two mirrors on your trike. Two mirrors allow you to see behind you during a tight turn in traffic. I use MirrorCycle mirrors - on the QNT they easily attach to the steering mounts. A quick glance gives a nice wide view of the road behind.

Brakes:

I had disk brakes on my first trike, and Sturmey-Archer drum brakes for my ICE QNT, which I actually prefer. I know this goes against common wisdom that disc brakes are superior, but this is not my experience. Although YMMV, for me disk brakes on a trike are 1) overkill 2) require constant changing of the brake pads, 3) wander out of adjustment fairly regularly 4) sqeal during hard braking or cornering (yes, even when properly adjusted), 5) complicate removing the wheel, 6) accumulate mud and grit when riding in ice, snow, or mud. At least that is my experience with them.

The hub brakes on the other hand are integrated into the hub and so make removing the wheel trivial. They do not require pad replacement until you have about 30,000 miles or more on them, although I have found that I can get substantially more milage out of them even here in the mountains. They have excellent modulation (no wobble or pumping during hard braking), and are outstanding in rain being completely imprevious to water, mud, and snow.  I really like these brakes - good modulation, good stopping power, trivially easy to adjust, and zero maintenance required.

The one point in favour of disc brakes however, is if illness has effected your hands such that you cannot grip very well. Since this is a problem for me, I installed good quality brake levers. With these, gripping stength is not an issue, so that a small amount of pressure is enough to create strong stopping force. I now use SRAM Spetra 7 carbon fibre brake levers. To reduce the strength required even further, I removed the stock brake lines and installed teflon coated lines which help reduce the friction. Into these I add a few drops of Phil Woods Tenacious Oil (available form any good bike store) every two weeks in dry weather and every two months in wet weather. Finally I adjusted the brakes and the levers so that the distance required to engage the brakes is very small. All in all this has allowed me to stop on a dime so to speak, even though my hand strength is low.

The next step is to install hydraulic brakes, which fortunately I have not yet had to do. The advantage to hydraulic brakes is that no strength at all need to brake. The disadvantage in my experience with them on bikes when I was still able to ride a bike, is that their reliablility is not great and they are complex (relatively) to repair. Small punctures in the fluid hose can really cause problems. So for me, good quality hub brakes with good quality brake levers and brake lines are reliable, simple, and completely trouble free. YMMV.

Horn:

I carry an Airzound horn - very very loud. Loud enough for people listening to their car radios to hear.  Loud enough for cell-phone-using drivers to look up from their important conversations about their hair. Loud enough to stop dogs in their tracks.  And loud enough to prove to a police officer that your trike can be heard as well as seen.

To attach the horn, I purchased a curved barend for a normal bike at a cost of $2. I then cut the bar end just long enough to fit the horn onto the end - about 2". Then I removed the grip shifter, slid the barend onto the handlebar, and reattached the grip shift.

As you can see from the pic, this places the hord button directly under my wrist when holding the grip shifter. So sounding the horn is fast and easy. I do not need to move my hand at all - just a flip of the wrist onto the horn's button. The air bottle for the horn is attached under the seat with electrical ties, and does not interfere with folding the trike for storage in a car's trunk. It has been secure there for the last 50,000 Km.

Flags - your trike should be visible

Take a look at the picture at right. Even without a flag my trike is easy to see with all the reflectors and LED lights all over it. So why use a flag on your trike? Because the highest point on a trike - your head - is lower than a child standing upright. It is lower than many car windows. To to be seen when you are beside a vehicle - flags are essential. I use two bright flags made out of flag cloth from a sailing store. Flag cloth made for sailboats does not tear or rip in the wind. It also comes in very bright reflective colours that can be seen from far behind. I mounted my flags on a day-glo orange/red flag pole at 6.8 feet and 5 feet above ground. I also sowed Ministry of Transport yellow tape around the outside of the flags which makes them light up like a Christmas tree at night when a car's lights shine on them.

Fenders:

Speaking of being seen - look at the picture of my horn above. Notice the yellow Ministry of Transport tape attached to my fenders. I use both front and rear fenders all year round, and have this tape on all of them, as well as across the back of the seat and on my homemade headrest. This, plus my bright yellow helmet and riding shirt and super bright front and rear strobe lights makes the trike very highly visible day or night. Let the road racers laugh - I want to be seen by cars and avoided.

Fenders are also IMHO necessary at all times. Why? Because unfendered wheels kick up a lot of small stones, slugs, worms, feces, small dogs, and other items directly into ... you. Not all fenders however are created equal. On my ICE QNT I use the excellent ICE fenders - a bit more expensive, but worth every cent. Once properly set up you never need to readjust them. And they pop off quickly if needed with an optional quick release. Greenspeed also makes excellent fenders. Good fenders are rigid, lightweight, adjustable front-to-back and left-to-right, and clear wide tyres with ease.

Helmet:

What can I say? There are riders who passionately swear that helmet wearing is uncomfortable. They quote "statistics" which talk about the injuries people sustain simply from wearing helmets. And on and on. They say it is their right to wear or not wear what they want. Sigh.

So let me just say this - I have travelled tens of thousands of miles by trike. Passing trucks have thrown up stones which have dented my helmet. Sub-humans (teenagers) have thrown beer cans at me from passing cars which bounced off my helmet. I personally would not go around the block on my trike without wearing a good quality protective helmet.